以下不属于生物圈范围的是( )
A:大气圈的底部
B:岩石圈的上部
C:水圈的大部
D:大气圈的顶部
The lecture mainly deals with the trouble young children have __________ right from wrong.
如图所示,已知R2=10Ω.开关断开时,电流表示数为0.6A;开关闭合时,电流表示数为0.9A.则电源电压为____ V,R1=____ Ω.
It may be necessary to stop ______in the learning process and go back to the difficult points in the lessons.