关于电流和电路，下列说法中正确的是

题干

关于电流和电路，下列说法中正确的是（）

A：只要电路中的电荷发生了移动，电路中就会产生电流

B：从能量转化角度来看，电源是把电能转化为其他形式能量的装置

C：串联电路中的开关控制整个电路，并联电路中的开关只能控制部分电路

D：在电源外部，电流的方向是从电源正极流向电源负极

上一题下一题 0.0难度选择题更新时间:2019-07-10 04:44:19

D

Animals are our good friends. Some are active and others are quiet. But do you know anything about the clever animals in the world? Just have a look!

Animals	Interesting facts
	Kelly is an African elephant. Now she is 19 years old. She lives in the zoo. Kelly has produced more than 100 paintings since last year. She has made over $3,500 for the zoo. Newspaper reporters wrote about Kelly, and then people went to buy her pictures.
	Nana is a clever black and white dog in England. He can do many things just like a human. He can walk on two legs and close the door. Also, he is able to get things for his master, such as newspapers and the TV remote control. What's more, he can sleep and use the quilt very well. No games are difficult for him!
	Koko is a 44—year—old chimpanzee. He has lived with human for tens of years and can “talk” to humans with his hands. He can do simple gestures* and that helps people to understand him.