____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/
_____in the united states ,st.Louis has now become the 24th largest -city/
A being the fourth biggest city B once the fourth biggest city C it was once the forth biggest city Dthe fourth biggest city it was

答案

应选A
B应改为once being the forth biggest city
C中it用的不对
D逻辑不通……
记住,此类句子逗号前面的成分是修饰逗号后面主语的