【判断题】【消耗次数：1】
若|A|=n, B?A, 则存在B到A的单射。
①
正确
②
错误
参考答案：
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相关题目
【多选题】
设 f: A ? B, g: B ? C, 且 f○g: A ? C 是双射。则下面结论正确的有：
①
f : A ? B 是单射的；
②
g: B ? C 是满射的；
③
f : A ? B 是满射的；
④
都有可能。
【单选题】
设A和B皆为n阶方阵，则下面论断错误的是()。
①
A与B等价的充要条件是rank(A)=rank(B)
②
若A与B等价，则|A|=|B|
③
A与B等价的充要条件是存在可逆阵P、Q，使A=PBQ
④
A可逆的充要条件是A等价于E<SUB>n</SUB>
随机题目
【多选题】
She expressed her opinions_____________ change their ideas.
①
so that
②
so as to
③
in order to
④
in order that
【多选题】
All the students in our school ____________ in the hall to hear a lecture.
①
collected
②
gathered
③
assembled
④
doubled
【多选题】
This story_____________ a very brave (勇敢的) young girl.
①
is to
②
is about
③
concludes
④
concerns
【单选题】
Computer are being used more and more____________ in the world today.
①
extensively
②
expensively
③
exclusively
④
exactly
【单选题】
Anger is a normal emotion that we all feel from time to time. Some people express anger openly in a calm reasonable way. Some explode with anger, and scream and shout. But other people keep their anger inside. They can not or will not express it. This is called repressing anger. Many doctors think that repressing anger is more dangerous to a person’s health than expressing it. They say that when a person is angry, the brain gives out the same hormones (荷尔蒙) as that are produced during tense and nervous situations. They speed the heart rate and raise blood pressure, so the person feels excited and ready to act. Repressing these feelings will only make the feelings continue, and this can lead to many medical problems. To prevent these problems, these doctors suggest letting the anger out by expressing it freely. But recently some other doctors question this. They say that people who express anger repeatedly and violently become, in fact, more but not less angry. And this could cause medical problems. However, some doctors say that both repressing and expressing anger can be dangerous. They believe that those who express anger strongly may be more likely to develop heart diseases, and that those who keep their anger inside may face a greater danger of high blood pressure. Doctors say the solution is to learn how to deal with anger. The first step is to admit that you are angry and to recognize the real cause of the anger, and then to decide if the cause is serious enough to get angry about. If it is, do not express your anger while angry. Wait until your anger has cooled down, and express yourself calmly and reasonably. Doctors also say that a good way to deal with anger is to find humor in the situation that has made you angry, for laughter is much healthier than anger.According to the passage, which of the following about hormones is correct?
①
Hormones will cause people to get anxious.
②
Hormones will increase when one gets angry.
③
The brain produces hormones when one’s blood pressure rises.
④
The brain produces hormones when one has medical problems.
【单选题】
It is no good ___________ to know what you dont know.
①
pretend
②
to pretend
③
pretending
④
pretends
【单选题】
Goats are being hired to do the work of people near San Diego. The fires that occurred in Hillborbough four years ago destroyed thirty homes, most of which have been rebuilt. While people were rebuilding the homes, the grasses and bushes were growing back. The area is now so overgrown in bushes that there is again a major danger of fire.The city government put up bids to remove the bushes. The lowest bid they received was $50,000—and that was if the city provided breakfast and lunch for the workers for the six weeks it would take to clear the overgrown area. The city only wanted to give unlimited coffee and a piece of bread a day for each person. When that offer was rejected, the city asked for help on its website.A sheepherder in Montanta and a goat-keeper in San Bernardino read about the city’s plight（困境）while surfing the Web. They both offered to do the job for $25,000. The city government chose the goat-keeper because he lived closer. When he was told that the city dump（垃圾场）was overflowing , the goat-keeper said, “No problem. My goats will eat everything in your dump, except the car engines, of course.” So, for another $5,000, the city killed two birds with one stone. If all goes well, they will invite the goat-keeper and his “family” back every three years. The goat-keeper said that he would probably visit San Diego while his goats were in the dump.What are the “two birds” that the city government kills with only one stone?
①
Both the sheepherder and goat-keeper will work for the city for $25,000.
②
The danger of fire and providing breakfast and lunch for the work crews.
③
The danger of fire and the overflowing dump.
④
The city government can save some money and the goat-keeper has a new job.
【单选题】
You have to work hard if you want to __________ in your courses.
①
achieve
②
succeed
③
win
④
beat