题型:选择题 Every Earth Day , We are made _____ signs to warn people to protect the nature .A.designB.designedC.to designD.Designing 查看答案
题型:单项选择题 已知双频阻波器频率为f1、f2(f1<f2)的回路对谐时,()A.L1、C1调谐于f1,L2、C2调谐于f2B.L1、C1调谐于f2,L2、C2调谐于f1C.L1、C1和L2、C2均调谐于f2,配C3时整组调谐于f1D.L1、C1和L2、C2均调谐于f1,配C3时整组调谐于f2 查看答案