英语翻译为什么空格里填的是couldn't have receiveds my e-mail,而不能直接填couldn'

Mary said they couldn't come on time,( 为什么空格里填的是didn't she My young brother couldn't work out the answer and ( ) 为什么填“n 是Have you decided ( ）on winter vacation?空格里为什么不能填what to do jenny couldn't get the car(),for it is too cold.为什么填moving的形 couldn't have done? I couldn‘t believe ） my eyes.中间填一个介词 I couldn't swim when I was yong.She couldn't,____ .怎么填? 英语翻译Mary couldn't have received my letter,or she should have 为什么My parents ( ) Beijing for ten years中间只能填have been in而不能填 Try ____ she might,Sue couldn’t get the door open.为什么填as?语法上 can’t / couldn’t have I couldn't eat up the rest 填介词 rice