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1933年与1929年相比，整个资本主义世界工业生产下降 $\frac{1}{3}$ 以上，贸易总额缩减 $\frac{2}{3}$ ，这说明1929年爆发的世界经济大危机（　　）

氧气是我们身边常见的物质，以下有关氧气的叙述正确的是（     ）

    Tom's school basketball game is next month. His class 1 a new player. His teacher asks him to be one. of the players 2 he is tall (高的). But Tom doesn't like 3 sports. He can't play basketball 4 and he thinks it is 5 for him, so he calls his friend Edward to help him. Edward says he'll help Tom 6 his basketball skills (技巧). They have about 20 days to prepare for (为……做准备) the game, and in the next three 7 they play basketball for 2 hours a day. They don't have much 8 at school, so they play it after the classes 9 .Tom is tired (疲倦的) but happy every day. Now, Tom loves 10 He thinks it is relaxing and fun.