____in the United States,St.Louis has now become the 24th largest city.

题目

____in the United States,St.Louis has now become the 24th largest city.
A being the fourth biggest city
B it was once the fourth biggest city
C once the fourth biggest city
D the fourth biggest city it was

答案

C
前面那个是不能有动词的,因为他是从句.所以可以选A,C
但是他后面又说圣路易斯变成了第24大城市,那就是说他 以前 是第四大,所以要用once而不是being