既能用排水法,又能用向上排空气法收集的气体是 [ ]
A.易溶于水,密度大于空气
B.易溶于水,密度小于空气
C.不易溶于水,密度大于空气
D.难溶于水,密度小于空气
答案:C
Would you please keep silent The weather report ()and I want to listen.
A.is broadcast
B.is being broadcast
C.has been broadcast
D.had been broadcast
请画出利用运放组成的PID调节器的原理图。