所以正确并熟练地使用以上听力真题中的虚拟语气的句型，尤其是其中的“if…would”这样最基本的虚拟语气句型，是拿到语法高分的一个很重要的因素。

【利用指数】★★★★★

高级语法使用(Higher Level Grammar)

七分必备语法之情态动词完成时：

【听力真题】

The early farmers kept various animals, including cattle and sheep. There’s also evidence of pigs, but it is possible that these could have been descended from the native wild species….so we must assume that form the beginnings of Neolithic farming the number of breeding sheep would have considerably exceeded three hundred, and the national catle erd must have been of a similar size…but this method would have severely restricted the range of the colonising fleets. The sheer volume of animal transport necessary means it’s unlikely that this livestock could have been brought from anywhere further than England…the body of the plough would have been of wood and could have been drawn by people, but it’s also likely that cattle were used… however, after the axe had been chipped into shape, they needed water and sand for grinding and polishing, so a high mountainside wouldn’t have been an appropriate place for this. So this final stage of the manufacture must have been carried out close to water and sure enough, there’s ample evidence of this at coastal sites… after firing, the outside was often polished. This would have helped the pots of retain water, as they weren’t glazed… this could have been an limitation of earlier vessels which were made of leather sewn onto wood.

【相关点评】
　
以上我们选取了剑桥6 test3 section 4中的听力原文进行分析，因为场景是关于新石器时代的畜牧，农耕和陶器制作等的讲座，所以需要大量地表达对过去事实的推测，因此我们可以听到频繁地出现了情态动词+动词完成时的结构：

Could+ have done：表示“过去本来可以做某事，但实际上没有做”

Would+ have done：表示对过去事情的假设，意思是“本来会做”

Must+ have done：用于肯定句，表示“过去一定做过某事”，表示一种很有把握的推测。

除此之外，还有类似的结构，如：

should (ought to) have done ：表示过去应该做而(实际)没有做的事情,含有责备或遗憾的语气，意为“本应该……”

needn’t have done：表示过去没有必要做某事，但实际上做了某事

may/might have done：表示对过去情况的一种不太有把握的可能性推测，表示“过去可能/大概已做了某事”

在雅思口语真题中，有大量题目都是针对过去发生的事情，所以需要表达对过去的各种推测的语气时，正需要这种结构，例如：

【真题举例】

Part 1：

When was the last time you gave flowers to someone?

What subjects are you studying?

Why did you choose to study that subject?

Part 2：

………………………………………………………………………………………………………………………………

Describe an antique or some other old thing that your family has kept for a long time.

You should say:

what it is

when your family first got this thing

how long your family has kept it

and explain why this thing is important to your family.