B的話應該改成NO matter how difficult English is.你的B項is位置放反了.空格, he would have been able to pass the exam. C.Had he studied harderD.Should he study harder 為什么D不行__no air ,there would be no sound.為什么是were there不是was there

1. should he study harder這是立足于現(xiàn)在，對將來的虛擬。而題干是would have been這是對過去的虛擬，所以時態(tài)用的是過去完成時。

2. 因為存在空氣，所以是虛擬假設不存在空氣，用were there，不用was，was不是虛擬。

只要是虛擬假設there都要加were嗎1.were表虛擬是跟現(xiàn)在事實相反的虛擬，跟there沒關(guān)系，比如：If i were you, i would go to Beijing university.如果我是你（這是對現(xiàn)在的虛擬，因為我不可能是你），我就去北大。If there were 3 apples, what would you do?如果有3個蘋果，你會怎么辦?(實際上沒有3個蘋果，只是虛擬)。2.請注意，were表示虛擬的時候，不能用was替代，比如：Were he a teacher, his mother would be so happy. √如果他是老師，他的媽媽會多高興啊。Was he a teacher, his mother would be so happy. ×這是錯誤地表達。3.另外if.+ 主語+were...的虛擬表達= Were +主語+...的表達（if省略了）。