题干

有两个人利用斜面共同将木箱拉上汽车,为了提高斜面的机械效率,下列做法中可取的是(   )

A:以较快的速度将木箱匀速拉上汽车

B:以较慢的速度将木箱匀速拉上汽车

C:改由一个人匀速将木箱拉上汽车

D:板长不变,改用光滑的斜面板将木箱匀速拉上车

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答案(点此获取答案解析)

D

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    People from every corner flooded into the streets that Christmas Eve. "Frosty the Snowman," and "Jingle Bells" 1 in stores; on the pavements, the street singers performed happily. Everyone was 2 by someone else, delighted and cheerful. I was alone.

    As one of 8 kids of a Brazilian family, brought up in America's crowded apartment, I'd spent several years searching for aloneness. Now,3, at 27, a college student after the 4 with my girlfriend, every cell inside me wanted to be alone,5  not at Christmas. My family had 6to Brazil and my friends were 7with their own lives. Dusk was approaching, and the fact that I had to return to my 8 home made me sad. Lights from windows blinked (闪烁), and I hoped someone would 9 from one of those homes to invite me inside with a Christmas tree decorated with shiny fake snow and 10 presents.

    At a market, I felt more 11 when people were buying lots of goods, which12 the gifts we received as children in my mind. I missed my family and wanted to cry for wanting to be alone and for having achieved it.

    Outside the church, a manger (小耶稣) had been set 13. I stood with others watching the scene, some of them 14 themselves, praying. As I walked home, I realized that leaving Brazil was still a painful experience as I struggled with 15 I had become in 15 years in America. I'd mourned (悲叹) the 16, but for the first time, I recognized what I'd gained. I was independent, 17 and healthy. My life was still ahead, full of 18.

    Sometimes the best gift is the one that you give yourself. That Christmas, I gave myself 19 for what I'd obtained up to now and promise to go forward. It is the best gift I've ever got, the one that I most 20.