题型：问答题 简答题 不定项选择已知地球表面空气的总质量为m，空气的平均摩尔质量为M，阿伏加德罗常数为NA，若把地球表面的空气全部液化且均匀分布在地球表面，则地球的半径增加△R。为估算△R，除上述已知量之外，还需要下列哪一组物理量（ ）A．地球半径RB．液体密度ρ C．地球半径R，空气分子的平均体积V D．液体密度ρ，空气分子的平均体积V 查看答案
题型：问答题 简答题 Expressing gratitude is an important form of good manners. Nowadays more and more people in China have found it’s high time to (1) a thankful heart for the young.Everyone likes to get praised and appreciated. Gratitude is the greatest of virtues, which lets others smile and makes the world more beautiful. You just need several minutes to write down a thank-you note, but it brings much joy to the (2) .We live in a society where we enjoy the different services of others. But (3) of them should be taken for granted.Gratitude is also a kind of (4) in life. In developing gratitude for every moment—for the simple joys and even for the (5) times—we come to truly enjoy and appreciate life. Then we are able to see the (6) that surrounds us.Try to write a thank-you letter to your parents for working hard to (7) you a happy life.Be grateful to your teachers because of their (8) with your studies and character building.Say thanks to your friends who (9) both your happiness and sorrow. We are sure it will bring them much joy and add (10) into your own life as well.第（4）空应选择（）A．attitudeB．feelingC．emotionD．sense 查看答案