正确答案为：
They are ducks.
一般疑问句：Are they ducks?
否定回答：No,they aren't.
Those are tomatoes
一般疑问句：Are those tomotoes?
否定回答：No,they aren't.
These are carrots.
一般疑问句：Are these carrots?
否定回答：No,they aren't
They are cucumbers.
一般疑问句：Are they cucumbers?
否定回答：No,they aren't.
This is a potato.
一般疑问句：Is this a potato?
否定回答：No,it isn't.
This is a sheep.
一般疑问句：Is this a sheep?
否定回答：No,it isn't.
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