Our math teather is very patient and explains things to us___ ___ ___ ___(一次又一次)。

time and time again
相当于again and again
含义为“一次又一次地”

4个空？

3个空俺会，4个就不会了。。。

once and again.
不知道为啥有四个空。

over and over again， 一次又一次。
三个空是again and again,

over and over again