如图所示，为中学物理课上一种演示气体定律的有趣仪器——哈勃瓶，它是一个底部开有圆孔，瓶颈很短的平底大烧瓶。在瓶内塞有一气球，气球的吹气口反扣在瓶口上，瓶底的圆孔上配有一个橡皮塞。 在一次实验中，瓶内由气球和橡皮塞封闭一定质量的气体，在对气球缓慢吹气过程中，当瓶内气体体积减小
时，压强增大20% 。若使瓶内气体体积减小2，则其压强增大
A．20%
B．30%
C．40%
D．50%
答案：D
此过程可以看做等温过程：设原来气体压强为p，
,解得：
，所以选D.
Communication between parents and children is becoming a serious problem. I read a 41 about it in the newspaper. Some children have killed themselves after 42 with their parents. I think this is because they don’t have a talk with each other. Parents now 43 more time in the office, 44 they don’t have much time to stay with their children. As time passes, they both feel that they don’t have the 45 topic to talk about. I want to tell parents to be more with your 46 , get to know them and 47 them. And for children, show your 48 to your parents. They are the people who love you. So 49 them your thoughts. In this way, you 50 have a better understanding of each other.
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