助动词包括：be (is, am, are, was, were, been, being)；
have (has, had, having)；
do (does, did)；shall (should), will (would)

" be + 动词不定式"可以表示下面几种意思:

1.命令或指示。例如：
No one is to enter the room without permission.

2.计划或安排。例如：
A new bridge is to be built over the river soon. 

3.可能。例如：
This kind of tree is to be found in that forest.

4.应该。例如：
Such people are to be criticized.

5.表示后来发生的事，可以用来表示一种命运。例如：
They said good-bye, little knowing that they were never to meet again.

Task:这一期你的任务一:仔细观察下面三个句子,指出各个句子中的＂be+动词不定式＂是上面五种意义的那一种。

1.The books are not to be taken out of the reading-room.

2.The expedition is to start in a week's time.

3.He was to regret the decision.

任务二:根据我给出的单词填空.

He ____the meeting, but he fell ill.(用attend填空)

答案：

1.命令或指示。
2.计划或安排.
3.表示后来发生的事，可以用来表示一种命运。
4.was to have attended
was (were) + 不定式完成式
这种结构表示“本来打算…，本来要…（而结果则没做）”。例如：
He was to have attended the meeting, but he fell ill.
他本来要参加会议的，但是生病了。（因此没参加）