在任一企业中同时存在着三种不同的控制层，保证有效完成具体任务的称为【 】控制层。
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滑准税是一种关税税率随进口商品价格由高到低而由低至高设置计征关税的方法，可以使进口商品的价格越高，其进口关税税率越低；进口商品的价格越低，其进口关税税率越高。( )
A. 对
B. 错
The main idea of this passage is（）
A. it is likely to make an enemy of your admirer
B. there are many solutions to the problems of dating
C. an admirer has feeling every bit as sensitive as our own
D. it is possible to discourage an admirer without hurting his feelings
From the first paragraph we can infer that in the US schools（）
A. students enjoy shooting
B. safety is a problem
C. students are eager to be solider.
D. students can make guns.
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