if引導(dǎo)的虛擬語氣應(yīng)該用什么時(shí)態(tài)?
1.if引導(dǎo)的虛擬口氣是不是只有兩個(gè)時(shí)態(tài),if+過去式,情態(tài)動(dòng)詞過去式+動(dòng)詞現(xiàn)在時(shí) 或 if+had+現(xiàn)在分詞,情態(tài)動(dòng)詞過去式+have+動(dòng)詞分詞 這兩種句型?
2.應(yīng)該怎么使用他們這兩種時(shí)態(tài)呢?我總分不清什么時(shí)候用過去式和什么時(shí)候用完成時(shí),
例如：if you were at home yesterday,i would come to see him還是 if you had been at home yesterday,i would have come to see him 應(yīng)該是哪個(gè)呢?
3.應(yīng)該怎么分辨if是引導(dǎo)虛擬語氣還是引導(dǎo)真實(shí)語氣啊?