If $$\log_4 x = a$$ and $$\log_{25} x = b$$, then $$\log_x 10$$ isa

A

$$\frac{a + b}{2}$$

B

$$\frac{a - b}{2 ab}$$

C

$$\frac{a + b}{2 ab}$$

D

$$\frac{a + b}{2(a - b)}$$