In the old days people lived in caves and they had to make a fire themselves warm. A. to

问题补充：

In the old days, people lived in caves and they had to make a fire themselves warm.

A. to keep

B. keeping

C. keep

D. kept

答案：

(答案→)A. to keep

B. keeping

C. keep

D. kept

解析：本题考查的动词不定式作目的状语，故选A