— I rang you at about nine,but there was no reply.

— Oh,that was probably________I was seeing the doctor. [ ]

A. why  

B. when

C. what  

D. that

读某内陆国家等高线地形图，完成下列问题。

该国灌溉农田的水源量相对较大的时期在（）

A.夏季和秋季

B.冬季和春季

C.春季和夏季

D.秋季和冬季