单位时间内，通过超声波传播方向垂直截面单位面积上的声能量，称为（）。
参考答案：声强
在①试管；②量筒；③蒸发皿；④锥形瓶中，能盛装碳酸氢铵固体在酒精灯上直接加热的仪器有 [ ]
A．①②
B．①③
C．①④
D．只有①
– Excuse me, could you tell me ________ for Hong Kong?
– The day after tomorrow.
A. when did you leave
B. when you are leaving
C. where you are going
