句型转换。

1. Are you ready for a quiz? (肯定回答)

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2. Mr. Smith is washing the dishes. (对划线部分提问)

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3. This is a bathtub, a shower. (变选择疑问句)

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4. These dishes are clean, dirty. (变选择疑问句)

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5. Is this a refrigerator or a stove? (回答stove)

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生活中的下列物质，属于纯净物的是 [ ]

A．天然气

B．蒸馏水

C．酸奶

D．加碘食盐