4. Given $x-\frac{1}{x}=4$, then the value of $x+\frac{1}{x}$ is (
(A) $2 \sqrt{5}$
(B) $\pm 2 \sqrt{5}$
(C) $3 \sqrt{2}$
(D) $\pm 3 \sqrt{2}$.
4. B

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