题目

I can well remember that I was once asked to deliver    41     speech titled A Real Test in My Life before the whole class at the age of 9! You can imagine how     42    (terrible) shy I was the moment I thought of that---with so many eyes    43   (fix) upon me. I had no   44   (choose) but to prepare for it ,though. First of all, I was to draft the speech, which was just a piece of cake for me, a good writer. But the hardest part   45     (lie) in my speech from my memory. The real moment began     46    I stood on the stage with my legs trembling an如图所示装置, 物体A在水平桌面上, 滑轮和绳子重力以及滑轮轴处的摩擦均不计. 当B物体重为10牛顿时, 它恰好能匀速下降. 若用一个水平向左的力拉物体A使其向左匀速运动, 则这个力的大小是 ： A. 5牛顿;　　　　　　　　B. 10牛顿;　　　　　　 C. 15牛顿;　　　　D. 20牛顿.