The stamp on the letter is an art from we can get a lot of cultural knowledge.A. whomB.

问题补充：

The stamp on the letter is an art, from we can get a lot of cultural knowledge.

A. whom

B. which

C. them

D. those

答案：

A. whom

(答案→)B. which

C. them

D. those

解析：考查定语从句.先行词为The stamp,当前面有介词时,指物只能应用which做引导词,故选B.