对于伙食账目清楚的集体食堂宜采用的膳食调查方法为()法;需要掌握精确的营养素摄入水平时宜采用()法。
参考答案:记账法;化学分析法
一列简谐横波沿x轴负方向传播,波速为v=4 m/s。已知坐标原点(x=0)处质点的振动图象如图(a)所示,在下列4幅图中能够正确表示t=0.15 s时的波形的图是( )
C
Why did the famous teacher use a $100 bill at his lesson ( )
A.Because he wanted to make the bill into a ball.
B.Because he used to drop a bill on the floor and stepped on it.
C.Because he was going to give the bill to one of his students.
D.Because he wanted to make the students know what value was.