按要求改写句子。1. This is a pen. (变成复数句子)
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2. There are seven boys in the picture. (就画线部分提问)
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3. This is a bus. (变成一般疑问句)
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4. These are children. (变成单数句子)
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1. These are pens.
2. How many boys are there in the picture?
3. Is this a bus?
4. This is a child.