A:①②③④
B:②③④
C:②④
D:②③
读图,完成下列各题.
门第不高的读书人可以凭才学参政始于( )
The biggest problem for most plants, which______just get up and run away when threatened, is that animals like to eat them.
如图1甲所示的振荡电路中,电容器极板间电压随时间变化的规律如图1乙所示,则电路中振荡电流随时间变化的图象是图2中的(回路中振荡电流以逆时针方向为正)( )