To develop more accurate population forecasts, demographers have to know a great deal more than now about the social and economic determinants of fertility.
正确答案是D。
我的问题是A选项错误的原因是它没有使用虚拟语态还是than后面没有对称地使用they do这个结构?
另外,想问问than这个词的用法。究竟than后面什么成份是可以省略的,什么是必须有的?
还请nn们不吝赐教。。。谢谢啊!
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