在化学反应3Cu + 8HNO3 = 3Cu(NO3)2 + 2X↑+ 4H2O中X的化学式为()
A:NO2
B:N2
C:NO
D:NH3
如图,能判断直线AB∥CD的条件是( )
—Are you going to buy a new camera?—Yes. But there are so many cameras that I can't decide______________.
小明同学在探究“电流和电阻的关系”实验中,当定值电阻R由5Ω换成10Ω后,为了使____ 的示数保持不变,他应将滑动变阻器的阻值____ .(填“变大”、“变小”、“保持不变”)