should 用法讲与练之二
用于表语从句中）
5. 用在 It is / was necessary/ important/ strange/ incredible 或 It is a pity/ a shame/ no wonder 之后由 that 引导的主语从句中， should 有应该、必须、竟然、居然之意。例如：
It is necessary that he （should） be sent there at once. 有必要马上派他到那里去。
It is strange that the wheel should turn so slowly.
真奇怪，这个轮子竟然转动得如此之慢。
It is a great pity/ shame/ that he should be so conceited.
真遗憾，他竟会这样自高自大。
九 . should have + - ed 分词结构用来表达下述意义：
1. 表示应该已经，本来应该，即过去该做某事但实际没有做，其否定式 shouldn't have + - ed 分词意为本来不应该。例如：
These cells should have been kept in somedry places. 这些电池本来应该放（保存）在干燥的地方。（但实际上没有把它们放在干燥的地方。）
You shouldn't have dept those cells in the damp place. 你本来不该把那些电池放在潮湿的地方。（但实际上已经把它们放到潮湿的地方了。）
2. 表示（估计）应该已经，大概已经，即对过去情况的推测。例如：
They left at nine， so they should have arrived （= probably have arrived） home by now.
他们是九点钟走的，现在应该已经到家了。
They should have finished their work， for they began to do it so early.
他们很早就开始工作，现在大概已经干完了。
3. 意为竟然已经，居然已经，即表示说话人对已经出现的事态感到惊奇、惊喜、怀疑。例如：
I'm surprised that he should have been so foolish. 我很奇怪，他竟然会这么傻。
I'm amazed that Mr Harris should have said nothing about the matter.
这件事，哈里斯先生竟然只字未提，对此我大为惊异。
It is wonderful that you should have achieved so much these years.
这几年你竟然取得如此大的成就，你真了不起。
此外， should 还可以出现在 should be doing sth 或 should have been doing sth 等句式中，表示应该正在或表示说话人的某种不满情绪。例如：
Why should we be sitting here doing nothing？ 我们干嘛坐在这里闲着？
You should be wearing a mask. 你应当戴着口罩。
She shouldn't be working like that. She is still so weak.
她不应当那样干。她身体还很虚弱。
You should have been waiting for us. Why haven't you？ 你应当等着我们的。怎么没有等？