couldn't=could not
couldn't x could(could = can的past tense)
couldn't =不能
--------------------------------------------
一些额外的资料=
1.could do with 将就;能对付;需要,该
2.couldn't care less 毫不在乎
3.couldn't help 不得不;忍不住
4.could / might just as well 不如;还是...的好
5.couldst 你能【旧】