________ a dozen applications ,he finally got a job as a sho

________ a dozen applications ,he finally got a job as a shop assistant .A.To send ...
________ a dozen applications ,he finally got a job as a shop assistant .
A.To send B.having sent
C.Sending D.Sent
为什么不是选C而是B
为什么是having sent ,而不是hading sent 发送这一动作不是在got a job 之前么?