They have a ___ baby.

问题描述:

They have a ___ baby.
A. a five month old
B. a fifth-month-old
C. a five-month-old
D. a five-months-old

选C
选项A,month->months
选项B,无此用法
选项D,在使用连接符做形容词词组时,数词后面的名词用单数形式,months->month