Question

Beijing is one of the many cities in the World that —— now develpoing programs to restore their

historical buildings. A. is B.has been C.have been D.are 答案是D. 为什么不能选其他的？请给我详细解释!谢谢

Answer 1

that 引导的是定语从句修饰先行词cities，所以从句中的谓语形式应与先行词保持一致。这是个特殊的题型。这种题有两个类型：
1.Beijing is one of the many cities in the World that —— now develpoing programs to restore their historical buildings.
2..Beijing is the only one of the many cities in the World that —— now develpoing programs to restore their historical buildings.
当one前面特指时，定语从句修饰的是one；当one前面无修饰词表示泛指，则定语从句修饰cities。
再比如：
Barbara is easy to recognise because she is the only one of the women who ____ the evening dress.
此空只能填wears ,定语从句修饰one，其谓语用单数。
明白了吗？

Answer 2

have/has been doing是现在完成进行时，强调了始于过去的一个动作对现在造成的结果和影响，并且该动作还在发生着，但句中缺少by far, by now, up to now, up till now等和它搭配的时间状语，故排除B和C；that=many cities是复数意义的主语，故用复数的助动词are 和现在分词构成了现在进行时。

Answer 3

先行词是one of the many cities时，定语从句的谓语动词和名词复数即many cities保持一致，因为题中的时间状语是now，所以要用are.
若先行词是 the only/ very one of the many cities时,定语从句的谓语动词和the only/ very one 保持一致,用单数。