题目

I’ve come back to check on a baby. Just after dusk I’m in a car down a muddy road in the rain, past rows of shackled (戴镣的) elephants, their trunks swinging. I was here five hours before, when the sun was high and hot and tourists were on elephants’ backs.Walking now, I can hardly see the path with my phone’s flashlight. When the wooden fence post stops me short, I point my light down and follow a current of rainwater across the floor until it washes up against three large, gray feet. A fourth foot twisted above the surface, tied tightly by a short chain and choked by ring of meta2．在“探究导体的电阻跟哪些因素有关”的实验中．同学们提出了下列几种猜想：猜想1：电阻可能与导体的长度有关；猜想2：电阻可能与导体的横截面积有关；猜想3：电阻还与导体的材料有关．小明设计了如图所示的电路图，在A、B间接入下表中待研究的电阻丝（电阻丝用电阻符号表示），电源电压U恒定．（以下空格填电阻丝的序号）若电阻受温度的影响可以忽略，要探究猜想1，应该选用电阻丝B和D进行对比实验．要探究猜想2，应该选用电阻丝B和C进行对比实验．序号材料长度（m）横截面积（m2）A锰铜合金丝10.5B镍铬合金丝10.5C镍铬合金丝11D镍铬合金丝20.5