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关于砌筑砂浆的说法，错误的是（　　）。

A.施工中不可以用强度等级小于M5的水泥砂浆代替同强度等级水泥混和砂浆
B.配置水泥石灰砂浆时，不得采用脱水硬化的石灰膏
C.砂浆现场拌制时，各组分材料应采用体积计量
D.砂浆应随拌随用，气温超过30℃时应在拌成后2h内用完
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土壤容重大于土壤密度。
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Life gets noisier every day and very few people can free from noise of some sort or another. It doesn′ t matter where you live--in the middle of a modern city, or a faraway village--the chances that you will be disturbed by jet aero planes, transistor radios, oil powered engines, etc. , are almost everywhere. We seem to be getting used to noise, too. Some people feel quite lonely without back-ground music while they are working.
Scientific tests have shown that total silence can be very frightening experience for human beings. However, some people enjoy listening to pop music which is very loud, and this can do harm to their eardrums(耳鼓). The noise level in some disco is far above the usual safety level for heavy industrial areas.
One recent report about noise and concentration(专心,) suggested that although a lot of people say that any noise disturbs their concentration, what really affects their ability to concentrate is a change in the level of noise. It goes on to say that a background noise, which doesn′ t change too much (music, for example) lnay even help people to concentrate.
From this passage, the pollution of noise
A.doesn'tmattermuch
B.hasbecomeworseeverywhere
C.hasbecomebetterinbigcities
D.hasbecomebetterinvillages
单项选择题
When did you last see a polar bear? On a trip to a zoo, perhaps? If you had attended a winter activity in New York a few years ago, you would have seen a whole polar bear club. These " Polar Bears" are people who meet frequently in winter to swim in freezing cold water. That day, the air temperature was 3℃, and the water temperature was a bit higher. The members of the Polar Bear Club at Coney Island, New York are usually about the age of 60. Members must satisfy two require-ments. First, they must get along well with everyone else in the group. This is very important because there are so many different kinds of people in the club. Polar Bears must also agree to swim outdoors at least twice a month from November through February.
Doctors do not agree about the medical effects of cold-water swimming. Some are worried about the dangers of a condition in which the body′ s temperature drops so low that finally the heart stops.
Other doctors, however, point out that there is more danger of a heart attack during summer swimming because the difference between the air temperature and water temperature is much greater in summer than in winter.
The Polar Bears themselves are satisfied with the benefits (or advantages)of cold-water swim-ming. They say that their favorite form of exercise is very good for the circulatory system(循环系统)because it forces the blood to move fast to keep the body warm. Cold-water swimmers usually turn bright red after a few minutes in the water. A person who turns blue probably has a very poor circula-tory system and should not try cold-water swimming.
The main benefits ( or advantages) of cold-water swimming are probably mental. The Polar Bears love to swim year-round; they find it fun and relaxing. As one 70-year-old woman says, "When I go into the water, I pour my troubles into the ocean and let them float away. "
The passage is mainly about .
A.agroupofcold-water-swimminglovers
B.thePolarBears'lifeinNewYork
C.doctors'ideasaboutcold-waterswimming
D.therequirementsofthePolarBearClub
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