5. should +动词完成式
A.此结构的肯定式表示应该做的事而没有做，否定式表示某种行为不该发生但却发生了。例如：
You should have given her more help.
你应该多给她一些帮助的。(但没有给)
B. 表示推测，意为“可能”，但可能性较小。例如：
He should have finished the work by now.
他现在该把工作完成了。(推测)
C. should / would have thought意为“本以为，本认为”。例如：
A: "Can you type?"
B: "Certainly."
A: "Well, I should have thought you wouldn't."
I should have thought she wouldn't agree.
我本来认为她不会同意的。
D. should have thought有时意为“认为，以为”，相当于should think，但表示更为委婉、谦逊或不肯定的语气。例如：
I should have thought it fairly good.
我以为它是很不错的。
E. should have + 过去分词用于虚拟语气：
Had you written him, you should have known the details.
6. ought to + 动词完成式
此结构表示某种过去应该做而没有做的事，或被忽略未做的某种明智行为。例如：
You ought to have returned the book earlier.(还晚了)
You ought to have refused her at the beginning, but now it is too late.
Note:
这里的ought to也可以用should代替。
Homework:用给出的动词填空,注意要选用正确的助动词和时态.
1.The boy____ the book so soon because it is difficult even to an adult. (read)
2.We___him the news because he knew it already. (tell)
3.If we had taken the other road, we ____earlier. (arrive)
4.I _____you might take this into consideration. (think)
5.You ____ her at the beginning, but now it is too late.(refuse)