Is Qinghai-Tibet Railway plays an important role in China’s railway history the topic tha

问题补充：

Is Qinghai-Tibet Railway plays an important role in China’s railway history the topic that you’re coming to?

A. it

B. that

C. what

D. this

答案：

A. it

(答案→)B. that

C. what

D. this

解析：句意为：青海至西藏的铁路在中国历史上扮演着重要的角色就是你要谈到的话题吗？本句的正常语序为: Qonghai-Tibet Railway plays an important role in China’s railway history is the topic that you are coming to. 所以此处应是主语从句，从句中不缺少成份。故答案应为B。