问题
单项选择题
If the population of the Earth goes on increasing at its present rate, by the middle of the 21stcentury we______all the oil that drives our cars.
A．will use up
B．will have used up
C．have used up
D．will have been using up
答案
参考答案：B
解析：到将来某一时刻为止已发生了的动作，要用将来完成时。一般说来，如果句中有by引导的时间状语，谓语就应用完成式，并根据具体时间确定是现在、过去还是将采完成式。如：by now(现在完成式)；by l960(过去完成式)；by 2010(将来完成式)。