Poor housing and unemployment are the ______problems.

Poor housing and unemployment are the ______problems.
A、main
B、mains
C、main’s
D、mains’
【正确答案】：A
【题目解析】：限定参考范围的形容词如chief，joint，lone，main，only，principal，sole，very等，只能做前置定语修饰名词。