唐太宗曾兴奋地说：“天下英雄，入吾彀中矣！”使他得以实现这一愿望的主要工具是（    ）

   July 4 is the birthday of the United States of America. Since 1776, people have 1 the Independence Day holiday every year.
   What do people 2on Independence Day? Many colorful and interesting things. They have fireworks shows in the evenings and sing songs. Some families organize picnics with barbecues (烧烤). Kids can3much delicious food like hotdogs.
   And these parties are a good time to dress up. Some kids make July 4 hats 4 the stars and stripes(星条) of the country's flag on them. And Independence Day is in summer. Many kids use stars and stripes fans to keep themselves 5 .
   It's a great day, but no one forgets that it's6too. US people are proud of their   7  and proud of what the founders did for it. On Independence Day everyone gets the chance to show it.

在“研究平抛物体运动”的实验中（如图1），通过描点画出平抛小球的运动轨迹．

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