题目

阅读与表达(问答式) Dear Sonia,         I'm writing this letter in the classroom. It's snowing outside and I'm sitting by the window.         Some of the boys are playing on the playground. They are throwing snowballs to each other. Some girls are building a snowman, and some are chasing each other around the tree in front of the classroom. They are leaving footprints everywhere. Our teacher is shouting something loudly to them. In the classroom, some girls are drawing pictures.         What are you doing?                           13．如图所示，在试管内装些水，用橡皮塞塞住，加热使水沸腾．水沸腾后将橡皮塞冲出，这个过程中，水蒸气对橡皮塞做功，把内能转化为机械能．