单项选择题

一般性的规定是：在干燥的情况下，安全电压( )V。 A. 42 B. 36 C. 24 D. 12

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多项选择题

Which statement is correct for the concept of the word? A. Every word is a unity of the form and the meaning. B. Word is a cluster of letters between two blanks. C. A word is the fundamental unit of sentence structure. D. As for its internal structure, a word is the most stable unit in a language.

单项选择题

过一条正垂线作平面，不可能作出的平面是（）。