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问题 选择题

下列物质在变化过程中，只需克服分子间作用力的是

A．食盐溶解

B．干冰升华

C．氯化铵受热，固体消失

D．金刚石熔化

答案

答案：B

氯化钠是离子化合物，溶于水克服的是离子键。CO2是分子晶体，干冰升华克服分子间作用力。C发生化学变化，克服化学键。金刚石是原子晶体，熔化克服非极性键。答案选B。

单项选择题

In the following essay, each blank has four choices. Choose the best answer and write down on the answer sheet.
The purpose of the testing phase of software development is not to (21) the absence of errors in the programs being tested, but rather to find as many errors as possible. This statement may seem to contradict one’s intuitive notion of a successful test of a piece of (22) ; however, a successful test is one in which errors have been found, net one in which no errors have been detected.
There are generally two kinds of testing method: human testing and machine testing. In most companies where systems are developed, the first testing that occurs is not machine testing, but rather the detection of errors through (23) , team efforts, referred to as walkthroughs and inspection. With these methods, the author of the program forms a group with others who represent programming expertise or who may be part of the project team.
After code has been subjected to the manual testing described above, it is then machine test- ed. Again, the test cases are designed to detect the (24) number of errors. Incremental or integration testing occurs subsequent to unit testing. This means combing modules with those that have already been unit tested. The incremental approach not only tests the (25) of each module, but also the "rippling effects" of errors, and the interfaces among modules.

A) show B) exhibit C) findD) search
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单项选择题

正常运行中，润滑油温应保持在（）

A、20~35℃

B、30~45℃

C、35~45℃
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