Mary was hit by a car _____she was riding a bike to the zoo

问题描述:

Mary was hit by a car _____she was riding a bike to the zoo
A.when B.after C.until D.since

应该是A.
A是当…时候,B是在…之后,C是直到,D是由于,因为
句意:当玛丽骑车去动物园时,她被一辆骑车撞了.只有A才能表达“当…”的含义.