Consider a $$3 \times 3$$ symmetric matrix A such that two of its Eigen values are a $$\neq$$ 0 and b $$\neq$$ 0with respective Eigen vectors $$\begin{bmatrix}x_{1} \\x_{2}\\ x_{3} \end{bmatrix} $$ , $$\begin{bmatrix}y_{1} \\y_{2}\\ y_{3} \end{bmatrix} $$.  If a $$\neq$$ b, then $$x_{1} y_{1}+ x_{2} y_{2}+ x_{3} y_{3 }$$ equals

A

a

B

b

C

ab

D

0