“当非限制性定语从句的谓语是一个复合结构时,只能用which引导定语从句.”是什么意思?“谓语是一个复合结构”是什么意思?

在下列情况下要用 which:
①在非限制性定语从句中.
【例】
She made great progress and won a prize,which gave us a surprise.她取得了很大进步并获得了奖金,这使我们很惊讶.
Mrs Tailor's cat,which was very old,became ill and then died.泰勒太太的猫很老了,生病以后就死了.
②在介词+关系代词引导的定语从句,必须使用which.
【例】
This is the knife with which John hurt somebody.
这就是约翰伤人的那把刀.
He built a telescope through which he could see things far away.他建了一个望远镜,通过它,他可以看见远处的东西.
③当先行词本身是that时,使用which.
【例】
The predicate is that which is said of the subject.
谓语是对主语的陈述.
④当关系词后面有插入语时.
【例】
Here is the ALD which,as I have told you,is a great help to you.这是《牛津高级学者字典》,正如我告诉你的那样,对你会有很大的帮助.
⑤当非限制性定语从句的谓语是一个复合结构时,常使用which引导.
【例】
Little Bob always tells a lie,which his parents find strange.
小鲍勃总是说谎,这使他的父母感到很吃惊.
谓语由动词构成,依据其在句中繁简程度可把谓语分为简单谓语和复合谓语两类.
复合谓语可分为两种情况：
第一种是由情态动词,助动词+不带to的动词不定式构成的复合谓语：
What does this word mean?
I won’t do it again.
I’ll go and move away the bag of rice with Lin Tao.
You’d better catch a bus.
第二种是由连系动词+表语构成的复合谓语.例如：
You look the same.
We are all here.
The weather gets wamer,and the days get longer.
Keep quite and listen to me.
He looked worried.
We have to be up early in the moming.
Is Bill in?
School Is over.Let’s go home.
My pen is in my bag.
I feel terrible.
I* fell tried all the time.
He seemed rather tired last night.