题型:单项选择题 The people for the experiment were chosen completely ______.A.at lengthB.in essenceC.at randomD.in bulk 查看答案
题型:不定项选择 一理想变压器原、副线圈的匝数比为n1:n2=1:2,电源电压,原线圈电路接入一熔断电流I0=1A的熔丝,副线圈中接入一可变电阻R,如图所示,为了使熔丝不致熔断,调节R时,其阻值最小不能小于 [ ]A.440Ω B.440ΩC.880Ω D.880Ω 查看答案