题目

阅读下面短文，在空白处填入一个适当的词，或填入括号中所给单词的正确形式。 Aboutten years ago when I was at university, I worked at my university's museum.One day I was working in the gift shop, I saw two old people come witha little girl in a wheelchair (轮椅). AsI looked closer this girl, I realized she had no arms or legs, just ahead, neck and body. She was (wear) a little white dress. When the oldpeople pushed her up to me, I was looking down at the desk. I turned my headand gave (she)a smile. As I took the money from her grandparents, I looked back a如图所示，某同学用一个动滑轮匀速提起一袋质量为18kg的面粉，所用的拉力为100N，则动滑轮的机械效率为____．若用此动滑轮匀速提起一袋质量为25kg的大米，当拉绳子的速度为____m/s时，拉力的功率为54W(g取10N/kg，绳重与摩擦不计)．