7．Honeybees are disappearing for unknown reasons around the United States．Last winter，bees disappeared from 23percent of American beekeeping businesses．Causes of the phenomenon，however，have remained a mystery．
Now，scientists from several universities and the United States Department of Agriculture say they have a possible explanation for the bee decline．It is a little-known virus called Israeli acute--paralysis virus （IAPV）．The virus kills bees．Researchers in Israel first described it in 2004，but until now，bee experts haven't paid much attention to it．
When trying to find out why the bees were disappearing，a research team at Columbia University studied bee colonies （ 群體），some with and the others without decline．The research turned up large numbers of two types of fungi （真菌） once suspected of causing the bee decline．The research results，however，showed that the fungi were almost as common in colonies without a decline as they were in colonies with a decline．The researchers concluded that the two fungi probably weren't the cause．
Studies of the presence of IAPV，however，showed more interesting information．In those studies，done by a team at Pennsylvania State University in University Park，the virus showed up in 83percent of samples from colonies with symptoms （癥狀）．Only five percent of samples from symptomless colonies had it．
Scientists still don't know whether IAPIV can single--handedly cause the bee decline．They believe that even if the virus is making colonies sick，it could have a partner in crime．It's possible，for instance，that insects or chemicals in the environment weaken bees，making them more likely to catch IAPV．
Scientists are still trying to figure out how IAPV came to the United States．The United States currently allows bee products to be imported from Canada，Australia，and New Zealand．If it turns out that this trade is spreading disease，the rules might eventually change．
46．According to the passage，IAPV is a virus thatA．
A．hasn't attracted much attention
B．well-known to doctors and scientists
C．was first found by Austrian researchers
D．is dangerous to animals and human beings
47．The underlined word decline in the second paragraph most probably meansB．
A．disease B．decrease C．secret D．growth
48．From the third and fourth paragraphs，we know researchers draw their conclusions by means ofC．
A．calculating B．examining C．comparing D．investigating
49．The underlined sentence in the fifth paragraph probably meansC．
A．the virus could also cause other damages
B．there must be something that is the real cause
C．IAPV is not the only cause for the bee decline
D．the virus may be caused by the polluted environment
50．What still remains unknown to American scientists according to the passage？D
A．How and why to kill IAPV．
B．How to change the rules of the bee products trade．
C．Whether bee products should be imported．
D．How IAPV came to America．
分析 本文講述了一種新型的叫做IAPV的病毒引起了美國的蜂群的消失，而具體的影響途徑仍就在研究之中，科學(xué)家們甚至不清楚該病毒的來源．
解答 46．A 細(xì)節(jié)理解題．根據(jù)文章第二段內(nèi)容..virus called Israeli acute--paralysis virus （IAPV）．The virus kills bees．Researchers in Israel first described it in 2004，but until now，bee experts haven't paid much attention to it．蜜蜂的消失可能是IAPV病毒導(dǎo)致的，但該病毒到現(xiàn)在并未引起重視，故選A．
47．B 詞義猜測題．文章第一段表明蜜蜂無故的消失，說明蜜蜂數(shù)量的減少，后文專家對該現(xiàn)象做出解釋，聯(lián)系前后，劃線單詞應(yīng)表示減少，與B選項同意．
48．C 推理判斷題．文章第三段和第四段可得知，研究人員對蜂群和真菌的種類都進行了對比，以找出蜜蜂消失的確切原因，由此判定C為正確答案．
49．C 推理判斷題．根據(jù)文章內(nèi)容Scientists still don't know whether IAPV can single--handedly cause the bee decline．They believe that even if the virus is making colonies sick，it could have a partner in crime 科學(xué)家不能確定IAPIV是唯一的原因，且劃線部分表示有一個犯罪時的搭檔，詞句表明引起蜜蜂消失的原因不止一個，故C為正確選項．
50．D 細(xì)節(jié)理解題．由文章最后一段的第一句話可得知Scientists are still trying to figure out how IAPV came to the United States 答案為D．
點評 本文是健康環(huán)保類閱讀理解．做這類題材閱讀理解時要求考生對文章通讀一遍，做題時結(jié)合原文和題目有針對性的找出相關(guān)語句進行仔細(xì)分析，結(jié)合選項選出正確答案．推理判斷題也是要在抓住關(guān)鍵句子的基礎(chǔ)上合理的分析才能得出正確答案，切忌胡亂猜測，一定要做到有理有據(jù)．
