I saw some trees the leaves of were black with disease.A. thatB. whichC. itD. what

问题补充：

I saw some trees the leaves of were black with disease.

A. that

B. which

C. it

D. what

答案：

A. that

(答案→)B. which

C. it

D. what

解析：考查定语从句。先行词为some trees，当做介词宾语时，指物的引导词只能使用which，故选B。