6 Given that $x_{1}, x_{2}$ are the real roots of the equation
$$
x^{2}-(k-2) x+\left(k^{2}+3 k+5\right)=0
$$
( $k$ is a real number)
the maximum value of $x_{1}^{2}+x_{2}^{2}$ is
(A) 19 ;
(B) 18 ;
(C) $5 \frac{5}{9}$;
(D) does not exist.