他改变了中国战争的性质，也改变了外来援助的结构．英美对日宣战和中国对轴心国的宣战，使亚洲的战争成为一场世界规模的反侵略和反独裁斗争之组成部分．可见，“它”是（　　）

    What do you do at the weekends? Some people like to1 at home. But others like to go for a walk2 play football. My friend Jack works hard in a factory on3. At the weekends he always 4 different things. On Saturday he5 his car and on6 he goes with his family to a village by car. His uncle and aunt have a farm there. It's not a7 one, but there's always8 to do on the farm. The children help with the animals and give them their9. Jack and his wife help in the field. At the end of the day, they are all10 and want to have a big meat very much.

为了探究“肉汤变质的原因”，小明同学做了如下的实验：将甲、乙、丙三套装置如图所示连接好，分别用酒精灯加热至肉汤沸腾15分钟，然后将甲、乙装置放在室温为25°C的环境中，丙装置放入冰箱中．三天后，甲装 置中的肉汤变质了，乙、丙装置中的肉汤未变质．请据此分析回答问题：