表示我国人口分布疏密的地理分界线是（ ）

小明同学在倒置的漏斗里放一个乒乓球，用手指托住乒乓球，然后将手指移开同时从漏斗口向下用力吹气，如图所示，则乒乓球（　　）

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二氧化碳气体若被加压、降温到一定程度，就会____ （填一种物态变化）成白色的像雪一样的固体叫干冰．干冰具有很好的制冷作用，在常温下迅速 ____ （填一种物态变化）成为气体， ____ 热量，使水蒸气遇冷凝结成水滴或小冰晶，从而达到降雨的条件．

    A few years ago, I was eating dinner with my children before we went to a museum. We were talking ____ (愉快地) when a man walked up to me and asked if I had a ____dollars to give him. I replied that I didn't even have one coin on me. Of course, my kids stood up and said: “Yes, you do, mommy.” I was a little embarrassed because I felt as if they____(抓住)me not telling the truth. Normally, I don't carry lots of money in my ____, instead, I pay with my bank card everywhere I go.

    So I told the man I could u____my bank card to buy him something to eat. His disappointing____(表情) quickly changed into a smile. Then I went to get him some kinds of food. He thanked me when I h____him a bag of food. After he left. I had a talk____my children: "Usually, I don't always like giving money to everyone who asks for it. H____, I am not against meeting the needs of others as I____as I have it. "I felt good knowing that the man had a nice meal that evening.