题目

Vicky liked dog biscuits 【1】. She thought of a way to get the biscuits for herself.As a little dog, Vicky had learned to watch for the postman. Every day she went to meet him. He gave her all the letters. She brought these to Mrs. Smith—sometimes as many as six at a time. 【2】One day Vicky brought only one letter to Mrs. Smith. But the little dog looked excited about something. How happily her feet danced as she followed Mrs. Smith to the cupboard! She ran into the next room with the biscuit. 【3】 “How strange!” thought Mrs. Smith, “Why did the postman come back so soon?” B2013年我国探月工程向前迈进了一大步，“玉兔号”探月器成功探月.在“玉兔号”从距离月球5km高处减速降落时，“玉兔号”的重力势能______（减小/增大/不变），动能______（减小/增大/不变），该过程主要依靠大推力发动机提供的7500N反向推力完成，历时10min.若发动机始终提供竖直向上的反向推力，且“玉兔号”始终沿着竖直方向降落，则降落过程中，发动机共对“玉兔号”做功______J，做功的功率为______W.