The profile of the typical family in the United States is changing: a recent study shows that for the past decade, more children had mothers who were employed than had not.
A) had mothers who were employed than had not
B) have had employed mothers than had not
C) had employed mothers than not
D) than not have had mothers who were employed
E) than not had mothers employed
答案是D
more........ than not 是慣用語 (莫伯伯)
我想問為何B不行??

請高手指點