如图所示，用一根硬棒撬一块大石头，当在硬棒的A点上用竖直向下_爱下问搜题

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问题选择题

如图所示，用一根硬棒撬一块大石头，当在硬棒的A点上用竖直向下的力F₁压硬棒，石头未能撬起，则在力的大小不变的情况下，下列措施中最有效地把石头撬起来的是

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A．把垫着的小石头移近大石头，且用力的方向改为F₂所示的方向

B．把垫着的小石头移远大石头，且用力的方向改为F₂所示的方向

C．把垫着的小石头移远大石头，且用力的方向仍为竖直向下，即F₁所示方向

D．把垫着的小石头移近大石头，且用力的方向仍为竖直向下，即F₁所示方向

答案

答案：A

完形填空

Yesterday was my stepmother’s birthday. I haven’t been home for a long time, so I wanted to stop by the house to 36 her on this special day. I have been 37
on a low income so I was afraid that I couldn’t afford the long 38 . Gas is so expensive nowadays! 39 , I filled my tank with gas and set off.
I 40 at a shopping mall and found a present. It was the 41 gift and I knew she would love it. 42 when I got to the cashier, my card was 43 !
I didn’t have enough money to 44 the gift!
So I thought about the 45 for a few minutes. I could put it back and get something 46 , but I knew there was 47 else in the store she would have liked as much. So, I transferred some money from my saving account and was able to buy the gift. It took a 48 part of my savings but I wanted her to have something special.
It turned out that she loved the gift and I 49 that even though I had spent almost all my money, my stepmother 50 the best. I was glad I gave her the best I could.
Before I 51 my parents’ house, my dad took me to one side and, with our secret handshake, he gave me some money. I hadn’t 52 anything to him about my financial 53 , but I guessed my dad just knew. When I got to the car, I saw the 54 he gave me was three times what I had spent on the gas and the gift! It shows that doing the right thing always comes with great 55 .

单项选择题

NB/T47013.3-2015标准规定，无缝钢管超声波检测扫查灵敏度（）

A、等于基准灵敏度

B、比基准灵敏度低6dB

C、比基准灵敏度高6dB

D、比基准灵敏度高12dB