情态动词can和could和need的用法

情态动词can和could和need的用法
can/could
表示能力 can表示现在的能力，could表示过去的能力。
表示请求 could不表示过去，只表示委婉、客气的语气，但回答时必须用can。
表示可能性一般用在否定句及疑问句中，could也可用于肯定句。
Although he is only four, he can play the piano.
尽管他只有4岁，但他会弹钢琴。
Can I use your computer for a while?
我可以用一会儿你的电脑吗？
—Could I borrow your bicycle? 我可以借你的自行车吗？
—Yes, you can./No, you can’t. 可以。/不行。
That can't be Mary, for she is in hospital.

那不可能是玛丽，因为她住院了。

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注意
can有时也用于肯定句，表示理论上的可能性或一时的情况。常译为“有时会”。
Mother can be very forgetful sometimes. 妈妈有时候特别健忘。
In general Tom is a good man, but he can be very hard sometimes.
通常来说，Tom是个好人，但是有的时候他很严厉。
辨析：can与be able to
(1) 表示能力时，can与be able to意义相同，但是can仅用于一般现在时及一般过去时，be able to可用于更多时态。
(2) 过去形式的could与was/were able to相比，could仅说明具备某种能力，而was/were able to则侧重通过某种努力达到某种结果，常译为“成功做到了”。
As a boy of ten, he can operate the computer skillfully.
作为一个十岁的小男孩儿，他能很熟练的操作计算机。
He was able to get out of the room when the fire broke out.
火灾发生时，他成功地逃离房间。

need和dare
need意为“需要”，dare意为“敢”，二者都既可作情态动词也可作实义动词，一般在疑问句和否定句中作情态动词用，在肯定句中作实义动词用。
—Need he go yesterday? 他需要昨天去吗？
—No, he needn’t. 不，他不需要。
She dare not go out alone at night. 她晚上不敢独自外出。

It’s 5：00 in the morning when the alarm rings in my ears．I roll out of bed and walk blindly through the dark into the bathroom．I turn on the light and put on my glasses．The house is still as I walk downstairs while my husband and three kids sleep peacefully．Usually I go for a long run，but today I choose my favorite exercise DVD insanity．Sweat pours down my face and into my eyes．My heart races as I face my body to finish each movement．As I near the end of the exercise，I feel extremely tired，but a smile is of my face．It’s a smile because the DVD is over，but a smile of success from pushing my body to its extreme limit．
Some people enjoy shopping，smoking，food，work，or even chocolate．But I need exercise to get through each day．Some shake heads when they see me run through the town．Others get hurt when I refuse to try just one bite of their grandmother’s chocolate cake．They raise their eyebrows，surprised by my “no thank you，” or by my choice to have a salad．Over the years，I have learned it’s okay to just say “no．” I shouldn’t feel sorry for refusing food that I don’t want to eat．
So what drives me to roll out of bed at 5：00 a．m．？What gives me the reason to just say to ice cream？Commitment．A commitment to change my life with a way that reduces daily anxiety，increases self–confidence and energy，extends life and above all improves my body shape．This is the point where a smile appears on my face as I look at myself in the mirror or try on my favorite pair of jeans that now fit just right．It’s through commitment and sweat that I can make a difference within myself inside and out．
1．Why is there a smile on the author’s face in the morning？
A．Because she sees her family sleeping peacefully．
B．Because she finishes her favorite exercise
C．Because she enjoys the interesting DVD
D．Because she feels a sense of achievement
2．Which of the following is true according to Paragraph 2？
A．She doesn’t like others r politely
B．She likes to make others surprised
C．Others don’t understand what she does．
D．Others try to help her by offering her food
3．What does the underlined word “commitment” in the last paragraph mean？
A．Good health B．Firm belief C．A strong power D．A regular half
4．What can we learn about the author from the text？
A．She acts in a strange way
B．She wants to look different from others
C．She aims to develop a good body shape
D．She has difficult getting along with others