A:细胞的分裂和生长
B:生活得到改善
C:经常体育锻炼
D:心情愉快
Nowadays, many countries are looking for ____ (renewable/renew) energy to protect the environment.
如图所示电路,电源电压一定。电阻R1的阻值为R2的2倍。当开关S1、S2都闭合时,电流表A1的示数为I1,电流表A2的示数为5I1。当开关S1、S2都断开时,电流表A1的示数为I1′。则I1′与I1之比为( )
读北方地区图,回答下列问题: