A.曲线运动一定是变速运动
B.变速运动一定是曲线运动
C.曲线运动一定是变加速运动
D.曲线运动可能是加速度不变的匀变速运动
AD
_______very late last night, my brother got up late and went to school without breakfast this morning.[ ]
A. Working
B. Having worked
C. Worked
D. To work
我们食用的大米,无论什么条件下都不能萌发,主要原因是( )
A.去掉了果皮
B.去掉了种皮
C.去掉了胚乳
D.破坏了胚