In the sentence "Isn't it very cold today _Yahoo, the fun begins _," the blank spaces require punctuation marks to improve its clarity and readability. ;
The correct punctuation marks for the sentences are a question mark after 'Isn't it very cold today' and an exclamation mark after 'Yahoo, the fun begins.' The final sentences should read: 'Isn't it very cold today? Yahoo, the fun begins!' This enhances clarity and expresses the intended emotions.
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