题目

Teenagers in England do many the same things as children in China．They enjoy sending messages on their mobile phones and they also like swimming, listening to the latest music, watching TV and surfing the Internet.     Let’s follow Sally, a British teenager, and spend five days with her during her school holiday The First DayAfterbreakfast，Sally’s  mother went out and lefther alone al home Dinner was at6：30 p．m．After that，shefinished her English homework Then she surfed the Internet． The Second DaySally and hermother paid a visit to their friends and went swimming togeth（2008?湖北模拟）一个内壁光滑、绝热的气缸固定在地面上．绝热的活塞B下方封闭着空气，这些空气分子之间的相互作用力可以忽略．在外力F作用下，将活塞B缓慢地向上拉一些．如图所示．则缸内封闭着的气体（　　）A．分子平均动能不变B．单位时间内缸壁单位面积上受到的气体分子碰撞的次数减少C．单位体积内气体的分子个数增加D．若活塞重力不计．拉力F对活塞做的功等于缸内气体内能的改变量