by the time she got to class,the teacher had already started teaching

问题描述:

by the time she got to class,the teacher had already started teaching
中的by the time可以用下面那个词代换
A.when B.as soon as C.since D.while

when啊
可以互换的.
当她到教室的时候,老师早已开始教学.
B项 一……就……通常出现在时间状语从句中吧
而since是引导一个完整的陈述句或者时间点 自从..
while后用过去进行时当..的时候 和when有区别 但不大
when后接一般过去时