题目

在“探究串联电路中的电流”实验中，某同学用电流表分别测出图中a、b、c三处的电流大小．为了进一步探究a、b、c三处的电流大小有什么关系，他下一步的操作应该是:A．将电源两极对调，再次测量a、b、c三处的电流;B．改变开关S的位置，再次测量a、b、c三处的电流;C．将图中两只灯泡位置对调，再次测量a、b、c三处的电流;D．换用不同规格的灯泡，再次测量a、b、c三处的电流.根据短文内容，回答问题。Some things can carry messages, for example, a sign at the bus stop helps you to know which bus to take. Signs on the door tell you where to go in or out. Have you ever noticed that there are a lot of signs around you and that you receive messages from them all the time?People can communicate on many other ways. An artist can use his drawing to tell about beautiful mountains, about the blue sea and many other things. Books are written to tell you about all the wonderful things in the world and also about people and their ideas.Books, magazines, TVs, radios and films all help us to communicate with others. They all help us to know what is going on in the world and what other people are thinking about.（1）What can help you if you want to know which bus to take?（2）What do the signs on the door do?（3）People can communicate in many other ways, can't they?（4）What can help us to communicate with others?（5）What do they help us to do?