阅读下面的短文，根据所给语境，按要求完成下列各题。
①After Pluto (冥王星) was found in 1930, people took it as the ninth planet in our solar system(太阳系). But it isn’t like other planets. It is smaller and has an strange orbit(轨道). On August 24,2006， scientists said,“Pluto is not a planet.”
About 2,500 scientists met in Prague（布拉格，捷克首都）. At first, some of them said that there would be 12 planets in our solar system. In the end, the scientists said that only Mercury（水）, Venus（金）, Earth, Mars（火）, Jupiter（木）, Saturn（土）, Uranus（天王）and Neptune（海王）are the planets in the solar system. ②Each of these planets has its own orbit, and of the planets is big enough to be a planet. Pluto’s orbit overlaps (重叠) Neptune’s and it is smaller than the other planets. ③So Pluto is classified(划归/分类) as a dwarf planet (矮行星), but no longer a planet in the solar system.
Students at school will have new schoolbooks to learn the new solar system!
小题1:根据①处完成下面的句子（每空一词）
Before people _______ Pluto in 1930, there were _______ planets in our solar system.
小题2:根据②出完成下面的句子（每空一词）。
Every planet not only has its own _______ , but also is ______ enough.
小题3:将③处译成汉语。
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时汽车停止（位置如图b所示）．若汽车的运动可看成匀减速直线运动，则根据题中提供的信息，可以估算出的物理量是( ) 
