you will understand them when you become a____in the future A.teacher B.parent

you will understand them when you become a____in the future A.teacher B.parent
you will understand them when you become a____in the future A.teacher B.parent

you will understand them when you become a____in the future A.teacher B.parent
首先我想说parent可以作单数用的,指父或母.
其次,如果没有上下文的话,前面的them更可能指的是父母（parents）它常以复数形式出现.
所以B

B.parent 家长, 指父母中的一个.

A.teacher

parent为复数概念，不能用a
所以选A

A。不过这种题说实话，实在算不上什么好题目。