语法题目请分析为什么不选A谢谢

问题描述:

语法题目请分析为什么不选A谢谢
“Have u seen David recently?"
"No.I guess he ( )away on vacation."
A.must has been
B.must be
C.might have been
D.may has been

因为情态动词后面应跟动词原形,选C