______life began on the earth is one of the biggest puzzles to scientists.

Please turn down the music, ______our neighbors next door will be disturbed.

When the environmentally friendly cars came onto the market, many people were eager to buy them ________ the price.

An official said the plan had also taken migrant workers into account, ________ medical care would be provided even if they didn’t have a stable job.

Now my hometown is not at all _______ a traveler who visited it ten years ago can expect.

He is such a lazy man_____ nobody wants to work with_____.

Beijing took steps to limit the kinds of high-risk of borrowing money from the banks that can create the high price of housing, ______ happened in the United States．
a．a(chǎn)s                 B．that               C．how      D．while

_________ the whole process for the studies of cancer took more than a year, the technology is moving so fast that it will soon take just weeks．

The Mekong River Commission has found no evidence ______ the dams on the upper reaches have an influence on the water flow downstream．

27．It was the President himself______ opened the door．