Let y = x be the equation of a chord of the circle $$C_{1}$$ (in the closed half-plane x c $$\geq$$ 0) of diameter 10 passing through the origin. Let $$C_{2}$$ be another circle described on the given chord as its diameter. If the equation of the chord of the circle $$C_{2}$$, which x + ay + b = 0, then a - b is equal to

A

10

B

-6

C

6

D

-2