Had he not been so busy taking diamonds,he would have felt the blow.

1。例句中，為何要把had提到句首，如此有哪些用途？

2。還想問一下老師， have done , 語氣由強到弱，如此排列對嗎？

在含有 had/were/should 的虛擬條件句中，可以省略if, 將 had/were/should 放在主語之前，構(gòu)成部分倒裝。

Had it not been for the captain，the ship would have sunk. 假如不是船長，船就沉沒了。

Were she my friend，I would ask her for help. 假如她是我的朋友，我就會請她幫忙。

Should he come tomorrow，I would tell you. 假如他明天來，我就對你說。

更多例句：

Should the journeyer return, this stone would utter speech.“行人歸來石應(yīng)語。”

Were it to rain tomorrow, we would put off the basketball match. 假如明天下雨的話，大家將推遲舉行籃球比賽。

Had she studied harder, she would have passed the exam.　倘若以前她好好學習的話，她就會考試及格了。

【注意】只有當 if 從句中含有should, were, had done 的狀況下（不包含 would 和could），才能提前并省略if。

have done —— 這類虛擬語氣形式，只不過用于不同人稱有什么區(qū)別（如 should 僅限于第一人稱）或意思不同，沒程度上由強到弱的差別。除此之外，may 可用于推斷，不需要于虛擬語氣。