按要求做题。

1. What's this? (改为复数句子)

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2. It's a tiger. (就画线部分提问)

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3. They,lions,are(.) (连词成句)

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4. a,It,tiger,is(.) (连成一句)

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5. They are monkeys. (就画线部分提问)

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交流电按其变化规律可分为哪几类？