问题
填空题
如果棱柱底面边数为n，那么这个棱柱的顶点有______个，侧面有______个，面有______个，棱有______条，侧棱有______条．
答案
棱柱有两个底面，所以底面边数为n时，那么这个棱柱的顶点有2n个，侧面有n个，面有n+2个，棱有3n条，侧棱有n条．
故答案为2n，n，n+2，3n，n．
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如果棱柱底面边数为n，那么这个棱柱的顶点有______个，侧面有______个，面有______个，棱有______条，侧棱有______条．
棱柱有两个底面，所以底面边数为n时，那么这个棱柱的顶点有2n个，侧面有n个，面有n+2个，棱有3n条，侧棱有n条．
故答案为2n，n，n+2，3n，n．
Directions: For each blank in the following passage, there are four choices marked A, B, C and D. Choose the one that is most suitable and write down the corresponding letter.
| What do we mean by a perfect English pronunciation In one sense there are as many different kinds of English as there are speakers of it. (21) two speakers speak in exactly the same (22) . We can always hear differences (23) them, and the pronunciation of English (24) a great deal in different geographical (25) . How do we decide what sort of English to use as a (26) This is not a question that can be (27) in the same way for all foreign learners of English. (28) you live in a part of the world like India or West Africa, where there is a long (29) of speaking English for general communication purposes, you should tend to acquire a good variety of the pronunciation of this area. It would be a (30) in these circumstances to use as a model BBC English or (31) of the sort. On the other hand, if you live in a country (32) there is no traditional use of English, you must take (33) your model some form of practical English pronunciation. It does not care very much which form you choose. The most (34) way is to take as your model the sort of English you can (35) most often. |
A．listen
B．hear
C．notice
D．find