题目内容

提高电力系统动态稳定的措施有哪些?

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为什么苹果、梨用铁刀切了以后,表面会变黑?

用数字式万用表判断二极管的好坏,应使用()。

A. 电阻档
B. ×1k档
C. 直流电压档
D. 二极管档

The ladder shall().

A. be secured in a position so that it rests firmly against the ship's side from which the discharge operations are carried out
B. have at least two replacement steps which are secured in position by a method different from that used in the original construction
C. have battens made of hardwood,or other material of equivalent properties,in one piece and not less than 1.80metres long provided at such intervals as will prevent the pilot ladder from twisting
D. have steps made of softwood,or other material of equivalent properties,made in one piece free of knots,having an efficient slip surface

试述萃取法的原理、特点及其运用?

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