A:5米
B:7米
C:10米
D:18米
假设摩托艇受到的阻力的大小正比于它的速率,如果摩托艇发动机的输出功率变为原来的2倍,则摩托艇的最大速率变为原来的( )
设y1=40.9,y2=80.48,y3=(12)-1.5,则( )
They had some ____ yesterday.
-Our city looks more beautiful!-Yes. Lots of trees and grass ______ since last year.