would和should的用法,虛擬語(yǔ)氣中有什么區(qū)別?
以括號(hào)中所給詞的適當(dāng)形式填空：
The petrol tank is empty.I ______(fill) it up before we left home.
答案是should have filled
請(qǐng)問(wèn)1、這道題是虛擬語(yǔ)氣嗎?
2、為什么不能用“would have filled”?
關(guān)于這個(gè)問(wèn)題的第2個(gè)例題：
Had electronic computers not being invented,many problems of space flight _____ now.
(A) would not have been solved
(B) would not be solved
(C) must not be solved
(D) should not have been solved
麻煩請(qǐng)問(wèn)B、C、D為什么不對(duì)？