You must have seen geese before.But did you know why they fly in a "V"formation?大神帮我看看这句话有什么错误

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You must have seen geese before.But did you know why they fly in a "V"formation?大神帮我看看这句话有什么错误
You must have seen geese before.But did you know why they fly in a "V"formation?大神帮我看看这句话有什么错误

You must have seen geese before.But did you know why they fly in a "V"formation?大神帮我看看这句话有什么错误
完成时have been和明确表示过去的词before不能一起用.