The correct answer is B, 'There are other ways to have fun; you could go to the park'. Because 'There are other ways to have fun' and 'you could go to the park' are both complete sentences on their own, they need to be separated by a semicolon (as in this example), a comma and a conjunction, or a period and capitalization. Answer choice C puts a period after 'fun' but does not capitalize the y in 'you', therefore it is incorrect.
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