B．表示一种推测（只用于肯定句中，语气比may要肯定得多）。
must have则表示对过去情况的推测。例如：
This must be Tom’s room. 这准是Tom的房间。
Jack must have gone there, hasn’t he? / didn’t he?杰克准是去过那儿了，对不对？
C．比较：have to也表示“必须”，但have to更强调客观需要，must着重说明主观看法。如：
We had to be there at 10 o’clock．我们得在10点到那儿。（客观需要）
We must be back before 10 o’clock．我们必须10点前回来。（主观认为）
有时也可互换：
We must / have to leave now．我们得走了。
must和have to的否定式即mustn’t和don’t have to意思完全不同。Mustn’t表示“不作某事”，有禁止的含义；don’t have to表示“不必要（作某事）”，含有“客观上无此必要”的意思。例如：
You mustn’t move someone if the person is badly hurt．如果这人受了重伤，你一定不要动他．
The person isn’t hurt at all. You don’t have to give him first aid．这个人根本就没有受伤，你不必给他进行急救。
2）need need作及物动词，和不定式连用：
need to do sth. 需要干某事
need也可做情态动词，主要用于否定句，即：
needn’t + v.不必干某事 例如：
You need to tell him the reason．你需要告诉他原因。
You needn’t tell him the reason. 你不必告诉他原因。
情态动词need也可用于疑问句，肯定回答对一般must，否定回答时用needn’t．
——Need I come？ ——Yes，you must．／No，you needn’t．
教学设计方案Lesson 29
Teaching Aims
1. Practise the dialogue.
2. Study the uses of same of the modal verbs.
3. Study the language points in the lesson.
4. Do the discussion practice in Part 2.
Step Ⅰ Revision and Warm Up
1) Revise ailments and parts of the body. the following; toothache, earache, headache, and stomachache. Say to the class:
I’ve got…and get them to complete the sentence. Point to parts of your body and say I’ve hurt my ( arm/foot/leg/back/hand).
2)You can ask the Ss for advice for all these ailments: ask what should I do? and encourage the class to make suggestions.
Step ⅡPresentation
Tell the Ss a story by saying that this morning when I was on my way to school, I saw an accident in the street. A man was knocked down by a bike. He was injured on his knees. (Teach the new words injure and knee here. ) Some people went to help and he was sent to the hospital soon. I think he will be all right soon.
Say to the Ss Today we’re going to read a dialogue and learn about another accident in the street.
Step Ⅲ Listening
1.T: Say to the Ss that Chen Wei and Susan are walking down the street when they see an accident. Let’s listen to the dialogue. After listening, you are going to answer two questions.
1). What was the accident?
2). What did the girl injure?
Get two Ss to answer the questions. Check the answers.
1). A child ran into the street and knocked a girl off her bicycle.2). Her knee hurts, her knees and her head hurt too.
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英语教案－First aid