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Answer:
C. 4 +√(x+5)
Explanation:
The sign between the terms changes to form the conjugate. The radical contents are unchanged.
The conjugate of 4 -√(x+5) is 4 +√(x+5).
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Additional comment
The utility of a conjugate is that the product of a number and its conjugate is the difference of two squares. The squares are intended to remove an undesirable feature of the number, its imaginary part or its irrational part, for example. Here, the product of the number and its conjugate would be ...
(a -b)(a +b) = a² -b²
4² -(√(x+5))² = 16 -(x +5) = 11 -x . . . . no longer contains a root