can 和must這些既可以表能力又可以表推測(cè)的情態(tài)動(dòng)詞在構(gòu)成反義疑問(wèn)句時(shí)是不同的,當(dāng)他們表推測(cè)的時(shí)候,比如he can't be at home.這個(gè)句子的反義疑問(wèn)句應(yīng)該由can后面的動(dòng)詞決定,所以用isn't he?當(dāng)can 表示能力的時(shí)候,如...he can't be at home.這個(gè)句子是表否定的吧，為什么不用is he？呢？的確前面是否定句，后面應(yīng)該用肯定。eg: He must be a docter,isn't he?所以你的句子應(yīng)該是He can't be at home, is he? 他一定不在家，是嗎？還有，你后面的那個(gè)句子應(yīng)該也是錯(cuò)的，應(yīng)該是：He isn't at home, is he ?他不在家，是嗎？You must have studied English for three years, haven't you? 這句中的must 是一定的意思，表推測(cè)。你學(xué)習(xí)英語(yǔ)已經(jīng)有三年了，不是嗎？You must have studied English for three years,didn't you?句中有明顯的表示過(guò)去的時(shí)間狀語(yǔ) ，反義疑問(wèn)句就只能用一般過(guò)去時(shí)，不可以用完成時(shí)。eg: she must have finished reading the novel last night, didn't she ? 這句里面有明顯的過(guò)去時(shí)間last night,所以用didn't.你這句里面沒(méi)有明顯表示過(guò)去的時(shí)間，但是for +一段時(shí)間也可以與一般過(guò)去時(shí)態(tài)連用，所以也可以用didn't來(lái)構(gòu)成反義疑問(wèn)句，意思跟上句一樣，但前面的句子是完成時(shí)態(tài)，所以最好還是用haven't you?希望你看得明白