题目内容：

Men have always wondered about the earth they live on and about the ①_____ above them.

         When early men looked at the night sky, they asked themselves a lot of questions. They looked at the moon, and wondered what this strange bright object in the sky was. They did not understand why it changed its shape from night to night. They looked at the stars and planets. They also wondered why some of them changed their positions, while others did not.

         ②他们也思考地球的形状。 Most early people believed the earth was flat.

         ③In different parts of the world, there were different ideas about the universe. The ancient Greeks were the first people to study the universe more scientifically. In the sixth century BC Pythagoras put forward the idea that the world was round. However, he could not explain why people at the bottom of the world did not fall off.

         It was not until the sixteenth and seventeenth centuries that scientists found the answers to some important questions. ④With the help of Galileo’s telescope, people could see the sky more clearly, and find the positions of the stars and planets. Finally in 1665, Isaac Newton explained to the world what gravity (重力) was and people at last understood why they did not fall off the earth.

1.在文中①处填写一个单词，使得句意完整、上下文通顺。___________________

2.根据文章内容回答问题。

What questions did early men ask themselves when they looked at the night sky? Write down one of them.

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3.将文中②句翻译成英语。

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4.将文中③句翻译成汉语。

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5.写出文中④句的同义句，每空限填一词。

Galileo’s telescope made _________________ for people to see the sky more clearly, and to find the positions of the stars and planets.