用适当的英语解释下列句子：
1. What is your sister?
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2. Hurry up, or you will be late.
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3. The girl heard from her new pen friend yesterday.
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4. He joined the League five months ago.
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5. Our class consists of 43 students.
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6. He stopped driving his car, but rode a bike instead.
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7. He apologized to me for being rude.
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8. We should save the boy's life at all costs.
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9. I am afraid Mr. Wang is not available at the moment.
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10. He drove so carelessly. As a result, he knocked into the tree by the road. (because of )