—I can't stop playing computer games.
—For your health, my boy. I'm afraid you _______.
A:can
B:may
C:must
D:have to
按照现代免疫概念来划分,下列物质中能引起免疫反应的是:( )
汽车以20m/s的速度做匀速直线运动,刹车后的加速度为5m/s2,那么开始刹车后2s与开始刹车后6s汽车通过的位移之比为 ( )
—Does the bookstore math books?—Yes. Do you want to______ one?