如图所示，使一薄钢条的下端固定，现分别用不同的力去推它，Fl=F3=F4＞F2，使其发生（a）、（b）、（c）、（d）各图中所示的形变，能说明力的作用效果与力的作用点有关的两张图是（ ）
A．ab
B．bd
C．ad
D．ac
影响力作用效果的三大因素为：大小、方向、作用点，
我们要看力的作用效果与力的作用点的关系，必须利用控制变量法，
在力的大小、方向均不变的情况下，只改变作用点的不同，
我们可以看出只有ad合适．
故选C．
Dear Sir/Madam, I am writing to 36 about the fat body of a(n) 37 I found in my ‘Vegetable Surprise’ last Thursday. It was 38 a surprise to me! A bad one, though. And even worse was that 39 when I realized only half of the white insect was left there on top of my green vegetables. I informed the 40 of my problem and I did not expect him to 41 and tell me that insects were a good source of protein. I am a vegetarian! In fact, I have eaten in your restaurant many times 42 and this is the first time I have been 43 . And I do not feel we should have been 44 for this meal, so I would ask you to 45 the cost. I await your reply. Yours faithfully, Mr. John Smith
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