— _____
— It's an apartment building.
A:What's your home?
B:Where's your house?
C:What kind of house do you live in?
D:Where's the home?
已知a→,b→满足a→•(a→﹣2b→)=3,且|a→|=1,b→=(1,1),则a→与b→的夹角为( )
两根材料相同的均匀导线x和y,x长为l,y长为2l,串联在电路中时,沿长度方向电势变化如图所示,则x、y导线的横截面积之比为( )