—You can't imagine fantastic fun online chatting is.—Really？But it may cause a lot of tro

问题补充：

—You can imagine fantastic fun online chatting is.

—Really？But it may cause a lot of trouble sometimes.

A. what A

B. how

C. why

D. so

答案：

A. what A

B. how

C. why

D. so

解析：imagine后接了一个由what引导的宾语从句，该宾语从句是一个“what＋adj.＋不可数名词＋主＋谓”结构的感叹句，故A正确。