单项选择题

In order to compensate for the loss of fertile topsoil，farmers have been（）.

A.planting less corn and soybean
B.putting fertilizers on their fields
C.preventing soil erosion
D.decreasing the supply of top soil

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To check population growth is necessary when（）.

A.there are decreasing productivity gains
B.there are increasing productivity losses
C.we are close to reaching the sustainability limits at a world level
D.people become a cost

单项选择题

What does the question ’How could you have nine wives？’imply？（）

A.The old man is too old to have nine wives.
B.The old man shouldn’t have had nine wives.
C.The old man could marry only once because he is member of the Church of Rome.
D.The old man could have only a wife for he is a Christian.