Have you ever noticed the color of the water in a river or stream after a heavy rainfall? What do you think caused this change in color? It is soil that has been washed into the river from the riverbank or from the nearby fields．

Components of Soil

Soil is made up of a number of layers（層），each having its own distinctive color and texture．The upper layer is known as the litter．It acts like a blanket．limiting temperature changes and reducing water loss．The topsoil layer is made up of small particles of rock mixed with rotten plant and animal matter called humus（腐殖質(zhì)），which is black and gives the topsoil its dark color．This layer is usually rich in nutrients，oxygen，and water．Below the topsoil is the subsoil，a layer that contains more stones mixed with only small amounts of organic matter．This layer is lighter in color because of the lack of humus．Beneath the soil lies a layer of bedrock．

Soil forms from the bottom up．Over time bedrock is attacked by rain，wind，frost，and snow．It is gradually broken down into smaller particles in a process called weathering．Plants begin to grow，and rotten materials enrich the topsoil．Most of the soil in Eastern Canada．for example．Was formed from weathered rock that was exposed when the ice disappeared 12,000 years ago．

Water Beneath the Soil

Surface water collects and flows above the ground in lakes，ponds，and rivers．Once in the soil or rock，it is called groundwater．Gravity pulls groundwater through the soil in a process called percolation（滲透）．Eventually the water reaches a layer called the water table．Under this is bedrock through which water cannot percolate．

As water percolates downward，it dissolves organic matter and minerals from the soil and carries them to deeper layers．This causes a serious problem because plants require these nutrients for growth．

Soil pH

Soil can be acidic，neutral，or basic．The pH of the soil is determined by the nature of the rock from which it was formed．a(chǎn)nd by the nature of the plants that grow and rot in it．

The acidity of rain and snow can lower the pH of the groundwater that enters the soil．By burning fossil fuels such as coal，oil and gasoline，humans have been contributing to higher levels of acidity in many soils．When fossil fuels are burned．gases are released into the air and then fall back to earth as acid rain．Acid soil increases the problem of carrying nutrients to lower soil levels．As nutrients are removed，soil is less fertile．Plants grow more slowly in acidic soil，and also become easily attacked by diseases．

1．The layer of soil that provides necessary nutrients for plant growth is called ________．

A．litter                    B．topsoil                 C．humus                   D．subsoil

2．According to the text，which of the following is NOT true?

A．Soil forms from weathered rock on the earth surface．

B．The deeper layer of soil is darker in color than the surface soil．

C．Air pollution is partially responsible for acid soil．

D．Groundwater tends to carry away nutrients for plant growth．

3．We can infer from the passage that the water table lies ________．

A．between the topsoil layer and the subsoil layer

B．in the subsoil layer above bedrock

C．between the subsoil layer and bedrock

D．in the bedrock layer beneath the subsoil

4．The underlined word “dissolve” is used to express the idea that organic matter and minerals from soil are ________．

A．rushed away into the river

B．cleaned and purified by water

C．destroyed and carried away by water

D．mixed with water and become part of it

請認(rèn)真閱讀下列短文，并根據(jù)所讀內(nèi)容在文章后表格中的空格里填入一個最恰當(dāng)?shù)膯卧~。注意：每個空格只填1個單詞。

Communication Principles

How you see yourself can make a great difference in how you communicate．“Every individual exists in a continually changing world of experience of which he（or she）is the center”．Many communication scholars and social scientists believe that people are products of how others treat them and of the messages others send them．But every day we experience the centrality of our selves in communication．A student，for instance，may describe a conflict with a teacher as unfair treatment：“I know my teacher doesn’t like the fact that I don't agree with his opinions，and that’s why he gave me such a poor grade in that class．” The teacher might say the opposite．Each person may believe that he is correct and that the other person's view is wrong．

The concept of serf originates in communication．Through verbal and nonverbal symbols，a child learns to accept roles in response to the expectations of others．You establish self-image，The sort of person you believe you are，by how others think of you．Positive，negative，and neutral messages that you receive from others all play a role in determining who you are．Communication itself is probably best understood as a dialogue process．Our understanding of communication comes from our interactions with other people．In a more obvious way，communication involves others in the sense that a competent communicator considers what the other person needs and expects when selecting messages to share．So，the communication begins with the self，as defined largely by others，and involves others，as defined largely by the self．

Communication Occurs almost every minute of your life．If you are not communicating  with yourself（thinking，planning，reacting to the world around you），you are observing others and drawing inferences from their behavior．Even if the other person did not intend a message for you，you gather observations and draw specific conclusions．A person yawns and you believe that person is bored with your message．A second person looks away from you and you conclude that person is not listening to you．A third person smiles（perhaps because of a memory of a joke he heard recently）and you believe that he is attracted to you．We are continually picking up meanings from others' behaviors and we are constantly providing behaviors that have communicative value for them．

More often than not，you may have hurt someone accidentally and you may have tried to explain that you did not mean that．You may have told the other person that you were sorry for your statement．You may have made a joke out of your rude statement．Nonetheless，your comment remains both in the mind of the other person and in your own mind．You cannot go back in time and erase your messages to others．Communication cannot be reversed（倒退），nor can it be repeated．When you tried to re-create the atmosphere，the conversation，and the setting，nothing seemed right．Your second experience with a similar setting and person made far different results．

--May I open the window to let in some fresh air?

--_________

A．Come on!　            B．Take care!　　　    C．Go ahead!　　        D．Hold on!

He told us whether _________ a picnic was still under discussion．

A．to have            B．having              C．have              D．had

I like this house with a beautiful garden in front，but I don't have enough money to buy _________．

A．one            B．it                 C．this             D．that

Ladies and gentlemen，please remain _________ until the plane has come to a complete stop．

A．seated              B．seating                  C．to seat               D．seat

--Have you _________?

--No．I had the wrong number．

A．got in              B．got away             C．got off                     D．got through

A great person is always putting others' interests _________ his own．

A．below              B．a(chǎn)bove               C．in                D．on

News came from the school office _______ Wang Lin had been admitted to Beijing University．

A．which              B．what                C．that                D．where

--How about your journey to Mount Emei?

--Everything was wonderful except that our car _________ twice on the way．

A．slowed down　          B．broke down                   C．got down                     D．put down