—How about your travel?—You can hardly imagine what difficulty we have had the vast deser

问题补充：

—How about your travel?

—You can hardly imagine what difficulty we have had the vast desert.

A. exploring

B. explored

C. to explore

D. explore

答案：

(答案→)A. exploring

B. explored

C. to explore

D. explore

解析：考查词组：句意：--你的旅行怎样？--你很难想象我们探索广阔的沙漠是多么的不易。

实际上we have had the vast desert.是修饰the difficulty的定语从句，词组 Have difficulty (in) doing sth，在...方面有困难，in可以省略，故选A.