不同周期的负荷有不同的变化规律，以下说法正确的是（ ）。
A. 第一种变动幅度很小，周期很短，这种负荷变动有很大的偶然性
B. 第二种变动幅度较大，周期也较长，属于这种负荷的主要有：电炉、压延机械、电气机车等带有冲击性的负荷变动
C. 第三种变动基本上可以预计，其变动幅度最大，周期也最长，是由于生产、生活、气象等变化引起的负荷变动
D. 以上均不对
查看答案
系统的单位调节功率是计及（ ）的调节效应时，引起频率单位变化时的负荷变化量。
A. 发电机
B. 变压器
C. 线路
D. 负荷
This essay is written to .
A. introduce to people a known use of green bananas
B. describe the author's unusual travel experiences in Brazil
C. tell people how he happened to discover the real center of the world
D. show how a respect for other civilizations will open our eyes
The man who wrote this essay was .
A. a Brazilian traveler in a part of his country he had never been to before
B. a Brazilian from Rio who had received his education in England
C. an American from New England traveling in Brazil
D. a Latin American driving through the mountainous area of Brazil
The author is now convinced that .
A. It is natural for all people to think of the center of the world as being somewherevery familiar to them
B. there can be only one center of the world and it is where he was born in NewEngland- people in other countries do not know this
C. there can be only one center of the world and it is the rock pinnacle in theBrazilian village but most Americans do not know this
D. there are two centers of the world, one in the United States in the cultural sense,and the other in Brazil in the geographical sense
微信支付 
支付宝支付