第72句：

I couldn't have won the award without your assistance.

六级词汇讲解:
couldn't have won意为“本来不会赢”，是虚拟语气的一种，表示对过去情况的假设。

六级考点归纳：
“情态动词+现在完成时”句型的用法很多。如:
1. must have + done sth.表示对过去可能发生的事情的推测，意为“肯定”。如:
Mary has gone to work，but her bicycle is still hers.She must have gone by bus.
玛丽已经去上班了，但是她的自行车还在这儿。她一定是坐公共汽车去的。

2. would like to have done sth.意为“本打算做某事”。如:

I would Tike to have read the article, but I was very busy then.

我本来想读一读那篇文章，但是当时太忙了。

3. needn't have done sth.意为“本没必要做某事”。如:

I dressed very warmly for the trip，but I needn't have done so.The weather was hot.
为了旅行，我穿得很暖和，但是其实没有必要穿这么多。天气比较热。

4. ought to/should have done sth.表示“本应该做某事，而事实上并没有做”。否定句表示“不该做某事而做了”。如:

1) You ought to have been more careful in this experiment.
在做这个试验的时候，你.本应该更细心一些。
2) He ought not to have thrown the old clothes away.
他本不该把那些旧衣服扔了。