计算：

“人生最美丽的补偿之一，就是人们真诚地帮助别人之后，同时也帮助了自己。”这告诉我们（   ）

     Joan is an American girl. She lives in China now. She is in my class. Her parents work in China, too, but her brother works in the U.S.A. He often writes letters to them. Joan likes Chinese class very much, and likes speaking Chinese with us after class. Her father teaches us English well. We all like his class. On Sundays, Joan goes to the People's Park with her father and mother. Sometimes she goes shopping with her mother. They like the Chinese food very much. It's a happy family.

如图所示为牵引力F和车速倒数 $\frac{1}{v}$ 的关系图象．若汽车质量为2×10³kg，它由静止开始沿平直公路行驶，且行驶中阻力恒定，设其最大车速为30m/s，则正确的是（   ）

68年来，新中国一个又一个奇迹的创造是数以亿计的建设者发挥撸起袖子加油干的结果。他们中有让中国“站起来”的奉献者，有让中国“富起来”的领头羊，有让中国迈向“强起来”的弄潮儿。从中我们深刻领会到（  ）

①人们以不同方式为国家创造价值，也实现了自己的价值

②国家和民族的前途命运决定着我们每一个人的前途命运

③每一个建设者的不懈努力必将让国家发生历史性的飞跃

④人民是历史的创造者，是决定国家前途命运的根本力量