题目

A great number of people can get injured or even killed resulting from a human stampede(踩踏). The bad thing is that a peaceful group of people can quickly turn into a crazy panicked crowd.      36   If you are in a crowd, the most important thing is to make yourself familiar with your surroundings and mentally notice the exits. No matter where you are, make sure you always know how to get out.     37     If you are in a crowd of moving people, wet or uneven ground can be slippery or dangerous, causing you to fall. Be aware of the general atmosphere of the event, as pa用如图所示的实验电路来“探究--影响电阻大小的因素”，电路中a、b、c、d是四种不同的金属丝．编号材料长度（m）横截面积（mm2）①镍铬合金0.80.8②镍铬合金0.50.5③镍铬合金0.30.5④镍铬合金0.31.0⑤康铜合金0.30.5⑥康铜合金0.80.8现有几根镍铬合金丝和康铜合金丝，其规格如表所示．为了便于探究和分析，实验中要利用控制变量法，要求都相对金属丝a 进行比较，因此电路图中金属丝a 应选上表中的________（用编号表示），b、c、d 应分别选上表中的________ （用编号表示）．