We also look for ways to review what we ________ (learn) since three years ago.
have learnt
【详解】句意：我们也想办法复习三年前学过的东西。根据 “since three years ago” 可知，此处用现在完成时 have/has done 的结构，主语 we 是复数形式，助动词用 have ，故填 have learnt 。
B
C
D
means______. 
B
C
D
