Turn the key at the back of the alarm clock once . . . twice . . . three times. At first the key turns easily. But as you keep winding, the key turns harder and harder. Finally the clock is wound as…
Scaly dinosaurs and flying reptiles disappeared from the earth about sixty-five million years ago—long before there were people. Yet there are pictures of these animals in books. How do we know…
As earth whirls along on its endless journey through space, it has a companion that is always beside it— the moon. The moon is a small planet. It is only about one-fourth as big as earth. The moon…
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