我放学回来时，买完我爱吃的烤卤鸭后，在电瓶车上，我发现装卤鸭的袋子鼓起来了。
When I came back from school, after buying my favorite roast duck, in the battery car, I found the bag filled with marinated duck bulging.
我把这件事告诉了妈妈，妈妈说，她可从来没注意过这种现象，这件事真是奇怪透了！但是，我却知道其中的原理，因为煮熟的热食物将塑料袋子内的空气膨胀起来的，是热胀冷缩的原理在作怪！
I told my mother about it. She said that she had never paid attention to this phenomenon. It was so strange! However, I know the principle, because cooked hot food will expand the air in the plastic bag, which is the principle of heat expansion and cold contraction!
你若不相信的话，不妨来做个试验：把一个瓶子里灌满冷水，在把它放在火上烧，水烧开后，再不马上拿出来的话，瓶子就要爆炸了，现在你懂了吗？
If you don't believe it, you can do an experiment: fill a bottle with cold water, put it on the fire and burn it. If the water is boiled and doesn't come out immediately, the bottle will explode. Do you understand now?