Question

There were dirty marks on her trousers ______ she had wped her hands. A.where B.which C.when D.that

Answer 1

这题选A
后面是一个定语从句，从从句结构上看，它的主谓宾是齐全的，所以不缺主谓宾语，而是缺定状补成分。
根据句意，她刚才用裤子擦手，那个地方留下了很脏的痕迹。从句指她擦手的地方，所以应该选where

Answer 2

A.where

在她裤子上,她用来擦手的(地方),有脏的痕迹.

Answer 3

where