如图所示,R1和R2是材料相同、厚度相同、表面均为正方形的导体,R1边长为2L,R2边长为L,若R1的阻值为8Ω,则R2的阻值为 ( )
A:64Ω
B:4Ω
C:16Ω
D:8Ω
My mother made some posters yesterday.( 改为一般疑问句)
Did your mother ____ ____ posters yesterday?
从生物的生活环境来看,生物进化的趋势是( )