They decided at the end of this month.A. to leaveB. going backC. travelD. not start out.

问题补充：

They decided at the end of this month.

A. to leave

B. going back

C. travel

D. not start out.

答案：

(答案→)A. to leave

B. going back

C. travel

D. not start out.

解析：句意：他们决定这个月底动身。不定式作宾语表示具体的将要进行的动作，decide后接带to的不定式作宾语，结合语境可知选A。