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问题 选择题

一列简谐波在t=0时刻的波形图如图12-2-8（a）所示，图（b）表示该波传播的介质中某质点此后一段时间内的振动图象，则(   )

图12-2-8

A．若波沿x轴正方向传播，（b）图应为a点的振动图象

B．若波沿x轴正方向传播，（b）图应为b点的振动图象

C．若波沿x轴正方向传播，（b）图应为c点的振动图象

D．若波沿x轴正方向传播，（b）图应为d点的振动图象

答案

答案：B

在图(b)的振动图象中，t=0时刻质点在平衡位置并向y轴的正方向运动，而图(a)的波形图却表明在t=0时刻，质点b、d在平衡位置，而a、c不在平衡位置，故A、C选项不可能正确.若波沿x轴正方向传播，质点b应向上运动（逆着波的传播方向在它附近找一相邻点，此点正好在它的上方，质点b就应跟随它向上运动），B选项正确.若波沿x轴正方向传播，同理可以确定质点d应向下运动.D选项错.

问答题

Our little boy came up to his mother in the kitchen one evening while she was fixing supper, and handed her a piece of paper that he had been writing on. After his morn dried her hands on an apron, she read it, and this is what it said:
For cutting the grass $ 5.00
For cleaning up my room this week $ 1.00
For going to the store for you $ 0.50
Baby-sitting my kid brother while you went shopping $ 0.25
Taking out the garbage $ 1.00
For getting a good report card $ 5.00
For cleaning up and raking the yard $ 2.00
Total owed : $ 14.75
Well, I’ll tell you, his mother looked at him standing there expectantly, and boy, could I see the memories flashing through her mind. So she picked up the pen, turned over the paper he’d written on, and this is what she wrote:
For the nine months I carried you while you were growing inside me, no charge.
For all the nights that I’ve sat up with you, doctored and prayed for you, no charge.
For all the trying times, and all the tears that you’ve caused through the years, there’s no charge.
For all the nights that were filled with dread, and for the worries I knew were ahead, no charge.
For the toys, food, clothes, and even wiping your nose, there’s no charge, son.
When you ______, the cost of my love is no charge.
Well, friends, when our son finished reading what his mother had written, there were great big old tears in his eyes, and he looked straight up at his mother and said: "Mom, I sure do love you. "
And then he took the pen and in great big letters he wrote: "PAID IN FULL. "

What do you learn after reading the passage (within 20 words)
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单项选择题

折旧在财务现金流量中是指( )。

A．现金流入

B．现金流出

C．现金净流入

D．不考虑项目
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