用如图所示滑轮组匀速提升重为200N的物体，人对绳的拉力为125N，不计绳重和摩擦，滑轮组的机械效率为____ ．如果人的体重为550N，拉动过程中绳始终未断裂，他用此滑轮组能提升的最大物重为____ N．

A: What can I do for you?
B:____
A: For your daughter ?Look , the shoes are really nice . Do you like them ？
B: Yes . But I'm afraid my daughter doesn't like the color . ____ 
A: Sure . There are different kinds of shoes over there . What color does she like ?
B: ____ And black is her favorite .
A: What size does she need?
B: Size 9. Let me see . Um ,this pair of shoes must fit her .____ 
A: They are not expensive ,only 199 yuan .
B: That would be fine .____ Here is the money .Thanks very much.
A: You're welcome.