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答案：C
解析：
Choice C is correct. First follow the order of operations to get the following.
4-4a-(5+a)(5-a)=-21-4a+a^2
Since the answer choices do not match this, look for more factors.
The factors of -21 that add to -4 are -7 and 3.
Therefore, the answer is (a-7)(a+3).
