因?yàn)檫@里can't表猜測(cè)或判斷,不可能的意思,所以反義疑問(wèn)詞應(yīng)該對(duì)問(wèn)題本身提問(wèn),而不是對(duì)判斷詞提問(wèn).所以AB是錯(cuò)的.
為什么C是錯(cuò)的?
首先我們來(lái)把原句恢復(fù)成陳述句:
They can't have been watching the football match this time yesterday.
注意,這里的can't表示不可能.
再變成肯定句：
They were watching the football match this time yesterday.
為什么can't have been watching對(duì)應(yīng)were watching?
原因是：因?yàn)槭莟his time yesterday,所以是過(guò)去時(shí)態(tài),如果變成can't be watching就變成現(xiàn)在時(shí)態(tài)了.為了表現(xiàn)推測(cè)的內(nèi)容是過(guò)去,所以要用can't have been doing,但這里絕對(duì)不是完成時(shí)態(tài),所以C是錯(cuò)誤的.