These postcards are . A. they B. theirsC. theirD. them

问题补充：

These postcards are .

A. they

B. theirs

C. their

D. them

答案：

A. they

(答案→)B. theirs

C. their

D. them

解析：they人称代词主格，他们；theirs 名词性物主代词，他们的；their 形容词性物主代词，他们的；them人称代词宾格，他们。句意：这些明信片是他们的。结合语境可知选B，名词性物主代词做表语。