一平面简谐波在弹性媒质中传播．当媒质中某质元经过平衡位置时，它的 （）

一个物体在x轴上作直线运动，位置随时间变化的关系为x=2+4t2(SI)，则t=2s时物体加速度大小为____________m/s2

It was ________of you not to disturb us while we were sleeping

Every boy and girl ___(treat) in the same way.

Don’t worry. This is the ________(desire)weight range for you health