题干

在下面一段文字给①②③处补写恰当的语句,使整段文字语意完整连贯,内容贴切,逻辑严密。每处不超过16个字。

材料:T型支架上,细绳拴着一颗小球。这是物理课上常见的实验装置——单摆。王亚平将小球拉升至一定高度后放掉,小球像着了魔似的,用很慢的速度摆动。随后,王亚平用手指轻推小球,小球开始绕着支架的轴心不停地作圆周运动。在地面,单摆的运动周期与摆的长度、重力和加速有关。但在失重的状态,没有了恢复力,           ①            。这时,细绳并没有给球拉力。手推小球,相当于给了小球一个初始速度,同时②              ,细绳拉力平衡离心力,小球便绕着支架的轴心做圆周运动。如果没有细绳的拉力,小球就做匀速直线运动。而在地面,空气的阻力使物体的速度越来越慢,③               。

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答案(点此获取答案解析)

小球就静止在原始位置|细绳又给小球提供了拉力|重力则使物体向下掉。

同类题3

阅读理解

    A few years ago, I took a sightseeing trip to Washington, DC. I saw many of our nation's treasures, and I also saw a lot of citizens on the street—unfortunate ones, like beggars and homeless folks.

    Standing outside the Ronald Reagan Center, I heard a voice ask. “Can you help me?” When I turned around, I saw an old blind woman with her hand extended. In a natural reflex (自然反射), I reached into my pocket, pulled out all of my loose change and placed it in her hand without even looking at her. I hated being disturbed by a beggar.

    But the blind woman smiled and said: “I don't want your money. I just need help finding the post office.” In an instant, I realized what I had done. I had acted with prejudice (偏见)---I had judged another person simply for what I thought she had to be.

    I hated what I saw in myself. This incident brought back my central belief. It reminded me that I believed in being humble (卑下的), even though I'd lost that belief for a moment.

    The thing I had forgotten about myself is that I am an immigrant (移民). I left Honduras and arrived in the US at the age of 15. I started my new life with two suitcases, my brother, my sister and a strong mother. Through the years, I have been a dish washer, roofer, mechanic, cashier and pizza delivery driver, among many other humble jobs. Eventually, I became a network engineer.

    In my own life, I have experienced many acts of prejudice. I remember a time at age 17---I was busboy (餐馆工), and I heard a father tell his little boy that if he did not do well in school, he would end up like me. I have also seen the same treatment of family and friends, so I know what it's like, and I should have known better.

    But now, living my American middle-class lifestyle, it is too easy to forget my past, to forget who I am and where I have been, and to lose sight of where I want to go. The blind woman cured me of my blindness. She reminded me of my belief in being humble, and to always keep my eyes and heart open.

    By the way, I helped that lady to the post office. And in writing this essay, I hope to thank her for the priceless lesson she gave me.

同类题5

阅读下边一首诗,完成后面问题。
                                                                                                                                    幽居初夏 陆游
                                                                                                                  湖山胜处放翁家,槐柳阴中野径斜。
                                                                                                                  水满有时观下鹭,草深无处不鸣蛙。
                                                                                                                  箨龙已过头番笋,木笔犹开第一花。
                                                                                                                  叹息老来交旧尽,睡来谁共午瓯茶。
       注箨(zé)龙,就是笋。木笔,又名辛夷花。两者都是初夏常见之物。瓯(ōu):杯子。