5. Given that $\left\{a_{n}\right\}$ is a geometric sequence, and $a_{n}>0, a_{2} a_{4}+2 a_{3} a_{5}$ $+a_{4} a_{6}=2025$. Then, the value of $a_{3}+a_{5}$ is ( ).
(A) 15
(B) 25
(C) 35
(D) 45
5.(D).

From $2025=a_{2} a_{4}+2 a_{3} a_{5}+a_{4} a_{6}=a_{3}^{2}+2 a_{3} a_{5}+a_{5}^{2}$ $=\left(a_{3}+a_{5}\right)^{2}$, we know the answer is (D).