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问题 单项选择题

相敏式过流保护是根据启动和短路时同样电流大，但电动机启动时（）的特点，采用同时检测电流的幅值和相位确定保护装置是否动作。

A、功率因数低

B、功率因数高

C、启动时间长

答案

参考答案：A

单项选择题

A real estate developer in Florida, desiring to protect his high-rise apartment building on the beach from hurricane damage, has planted sea oats in two rows in front of his building in order to encourage the development of sand dunes between the water and his building.
Which of the following, if true, casts the most doubt on the probable effectiveness of the developer’s plan ？（）

A. Sand dunes provide little protection for tall buildings against the wind, which is sufficiently powerful even in minor hurricanes to cause serious damage to buildings.

B. Sand dunes have been shown to provide effective protection against the storm surge, the pounding waves driven by hurricane-force winds onto dry land.

C. Although sea oats will lead to the growth of sand dunes over many years, it would be far faster to build concrete bunkers between the building and the water.

D. Hurricane insurance has become so expensive that many owners of beachfront property choose not to buy it.

E. The developer has invested in reinforced steel girders and shatterproof glass as a way of minimizing damage to his building in the event that a hurricane hits the area.
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单项选择题

劳务分包企业建设工程项目施工人员50人～200人的应设（）名专职安全生产管理人员；

A.1名

B.2名

C.3名

D.4名
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