滚子从动件盘形凸轮机构的实际轮廓线是理论轮廓线的()曲线。A.不等距  B.等距

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问题:

滚子从动件盘形凸轮机构的实际轮廓线是理论轮廓线的()曲线。

A.不等距 

B.等距

考点:注册公用设备工程师暖通空调及动力专业暖通空调及动力专业
题型:单项选择题

阅读理解。

    Space travel is nothing new. The first spacecraft with a human was sent up into space in 1961.

    Since then, people have not only traveled to space, but many of them have also lived there in

space stations for some time.

    The Soviet Union(前苏联) sent the first space station into space in 1971. This space station was

called Salyut I. Salyut I was designed as a place where people could live while they observed space

and did experiments. The first group of astronauts lived there for 23 days. The Soviet Union went on

to make seven more Salyut space stations. At about the same time, the United States built its own

space station, called Skylab.

    Astronauts visited and often lived in these space stations for a short time. However, it wasn’t until

the late 1980s when the Soviet Union sent the Mir space station that people began to live in space for

a longer time. Mir stayed in space from 1989 until 2001, when it was decided that the space station

was too old and no longer safe to live in.

    Living in apace stations seems to be fun, but astronauts face many problems. One of them is food.

All the meals on space stations are put together on Earth and sent there by space shuttle. Because the

food has to last a long time (sometimes up to three months), a lot of it has to be stored in cans. The

space station does not have a fridge, but it has a cool room to keep fruit and vegetables fresh. Astronauts

also eat many other foods such as dried meat that do not need special care.

    Without the help of gravity, sitting down to eat can be tough. Astronauts sometimes have to fix

themselves to the wall while eating. They also have to be very careful to that food does not float away.

1.Which of the following has the closest meaning to the underlined word “observed” in Paragraph 2?

A. Discovered                              

B. Checked        

C. Watched                                

D. Fixed

2.What can we infer(推断) from the passage?

A.Astronauts can never have a chance to eat fresh food when they live in space stations.

B.The Soviet Union sent a total of 9 space stations into space in the 1970s and 1980s.

C.Astronauts could live in the Mir space station for no more than three weeks.

D.Space travel has quite a long history of more than 60 years.

3.What is the best title of this passage?

A. Exploring Space                          

B. Space Travel

C. Living in Space                          

D. Space Stations

题型:单项选择题

最近某商场家电部欲经营某种商品,进货渠道有三种可以选择:外埠进货、市内批发进货和厂家进货。该商品销路存在三种形态,销路好的概率为0.3,销路一般的概率为0.4,销路差的概率为0.3。选用外埠进货渠道时,在三种销路下的收益分别为25万元、15万元、-17.5万元。选用市内批发进货渠道,收益值分别为17.5万元、12.5万元、2.5万元。选择厂家进货,收益值分别为22.5万元、17.5万元、7.5万元。请分析计算,回答下列问题。

选用外埠进货渠道的收益期望值为()万元。

A.6.5

B.8.25

C.13.75

D.18.57

题型:单项选择题

52名同学租船游玩,租小船,每只限载3人,租金105元;租大船,每只限载5人,租金160元(不可超载)。如何租船花费最少?

题型:单项选择题

试述大陆架的定义、宽度及其法律地位。

题型:单项选择题

下列说法正确的是

A.将盐酸和醋酸钠溶液混合后溶液呈中性,溶液中c(Na)=c(Cl-)

B.1 mol CH4分子中含有的共价键数目等于1 mol Na2O2固体中含有的离子总数

C.80℃的纯水的pH大于25℃的纯水的pH

D.等体积、等物质的量浓度的NaCl溶液中离子总数大于NaClO溶液中离子总数

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