—Have you decided to Xi’an? —Yes. I’ll go there by train. It’s much cheaper than by plane

问题补充：

—Have you decided to Xi’an?

—Yes. I’ll go there by train. It’s much cheaper than by plane.

A. when to go

B. how to go

C. where to go

D. whom to go

答案：

A. when to go

(答案→)B. how to go

C. where to go

D. whom to go

解析：考查宾语从句。根据I’ll go there by train.可知，是问的怎样去西安，故选B。