This amount (指前面提到的人數(shù)）屬于舊信息，故前置；if sea levels rose是新信息，故后置，正好與后面的a sea rise of only 50 centimetres相銜接。

在if-then這樣的結(jié)構(gòu)中，如果有兩個(gè)以上的if形成排比，就把if從句后置；如果有兩個(gè)以上的then,就把then后置：

The potential for runaway greenhouse wanning is real and has never been more present. The most dangerous climate changes may still be avoided if we transform our hydrocarbon based energy systems and if we initiate rational and adequately financed adaptation programmes to forestall disasters and migrations at unprecedented scales. The tools are available, but they must be applied immediately and aggressively.

再如：

If the introductory language for the list is an incomplete sentence —

? End the introduction with a dash；

? End each item in the list except the last item with a semicolon ；

? After the semicolon in the next-to-last item in the list, write“and”or “or”as appropriate； and

? End the last item in the list with a period.

所謂if從句的限定性，是指if從句起到補(bǔ)充說(shuō)明的作用，例如：

[Carl is trying to save a cat，who climbed onto a pole and could not come down. ] “Catch me if I fall，Emil”，he called back as he began his ascent.

這里的if I fall并非句子重點(diǎn)，但放在前面并不自然，因?yàn)樗闹饕饔檬茄a(bǔ)充說(shuō)明。

影響if從句位置的因素還有其他，需要通過(guò)觀察和體會(huì)，逐漸把握。

責(zé)任編輯：admin