A:-4
B:±4
C:-2
D:±2
关于东北平原的叙述,正确的是( )
—You look so tired. What's the matter?—I was so busy that I didn't go to bed 12 o'clock last night.
保护动物多样性最主要的措施是
将两只额定电压相同的小灯泡L1、L2串联在如图所示的电路中,闭合开关后,发现灯L1较亮,灯L2较暗,其原因可能是( )
下列说法正确的是( )