“娶妇山中不肯留，会朝山下万诸侯。古人辛苦今谁信，只风清淮入海流。”这首诗称赞的是三过家门而不入的治水英雄。他是（　　）

        I live in a big city with a lot of homeless people. Luckily there're small ways of helping them and you needn't have a lot of1. One way to help is to buy their monthly magazine. 2doing this one day, I got to3a young homeless man. He was often4the magazine at the train station.

        He was a poor farmer from another country. After a while, I discovered that his5was close to mine. It6that we were born in the same month.

        I met him last year7after his birthday, and after congratulating (祝贺) him, without8， I asked if he had a good day. He9and said that he hadn't really celebrated. I felt so10.

        I just couldn't bear the thought of (不敢想) this nice, young man being11on his 25th birthday with no presents, no cake, nothing! So I went home and looked in my yarn (纱线) basket. 12for me, I had enough yarn13. I set to work and knitted (编织) a14for the young man. The yarn had become a little dirty15I didn't knit very often. Then I washed the yarn so the scarf would be16when he got it.

      I met him on my own birthday as I was going shopping. I had17to meet him so I had18the scarf and a piece of my own birthday19around with me. He was very happy with these gifts and so was I. The20in his eyes was the best present he could have given me!

在“测定动滑轮机械效率”的实验中，小明用如图所示的动滑轮提升钩码，改变钩码的数量，正确操作，实验数据如下：

（1）实验时，用手____ 拉动弹簧测力计，使持在动滑轮下的钩码缓缓上升。
（2）第①次实验时测得动滑轮的机械效率为____ ．
（3）第③次实验时，钩码上升的速度为0.05m/s，则拉力的功率为____ W．静止时拉力F的大小____ （选填“大于”“小于”“等于”）1.7N。
（4）由表中实验数据分析可知，同一动滑轮，所提升物重增大，机械效率将____ （选填“增大”、“减小”或“不变”）．