2、3、4顺序入栈(起始为空栈)，只要栈不空即可出栈，不可能的序列是()。
A. 4、3、2、1
B. 2、1、3、4
C. 1、2、3、4
D. 4，3，1，2
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When the farmer began to walk, be felt very uncomfortable because ______ .
A. he put on a pair of wrong shoes
B. he was ill
C. he quarreled with his wife
To avoid worldwide water shortage in the future, the author suggests that we can ______.
A. incense rainfall
B. develop ways of reusing water
C. cut down the number of large cities
D. reduce the number of factories, which use large amount of water
The author thinks that ______.
A. we should have enough water if every large city purified and reused its water
B. even if we could purify and reuse the water, water shortage might still be a problem
C. most large cities in the world have succeeded in purifying and reusing their water
D. purifying water is the only way to deal with the problem of water shortage
质量链接口是质量问题的多发地带。()
A. 正确
B. 错误
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