If $$(x) = x^{2} + 6x + K_{1}$$ and $$g(x) = x^{2} + 5x + K_{2}$$ have common factor $$x - a =$$ then a =

A

$$K_{2} - K_{1}$$

B

$$K_{1} + K_{2}$$

C

$$\frac{K_{1} + K_{2}}{2}$$

D

$$2(K_{1} + K_{2})$$