A:took, would feel
B:had taken, felt
C:had taken, would feel
D:took, would have felt
设0<x<π2,则“xsin2x<1”是“xsinx<1”的( )
用一大小为10N的力压一弹簧,其长度为10cm,改为大小为20N的力拉弹簧,其长度变为16cm,若用10N的力拉弹簧,其长度为( )