若△ABC 中,(b -a )(b+a )=c2,则∠B=( )。
90°
There are _____ apples on the table. You can have one. [ ]
A. few
B. a little
C. little
D. a few
一辆小汽车做变速直线运动,它前一半路程的速度是V1=2m/s,后一半的速度是V2=4m/s,则这辆小汽车在整个路程中的平均速度为( )
A.3m/s
B.4m/s
C.6m/s
D.2.67m/s