Helen and Mary are good friends. often help each other.A. ThemB. TheirsC. TheyD. Their

问题补充：

Helen and Mary are good friends. often help each other.

A. Them

B. Theirs

C. They

D. Their

答案：

A. Them

B. Theirs

(答案→)C. They

D. Their

解析：人称代词的用法。they 代替前面所指的Helen and Mary，在句中作主语，用主格。故选C.