A:behavior
B:ability
C:education
D:background
—The land in the southwest of China is in great need of .—Yes, it hasn't rained for a long time there.
如图所示为一质点运动的位移随时间变化的图象,图象是一条抛物线,方程为x=﹣5t2+40t,下列说法错误的是( )