$a,b\in R$,roots of $x^2+ax+b=0$ are $\alpha,\beta$ and roots of $x^2+bx+a=0$ are $\alpha+k,\beta+k$ where $k\neq 0$.If $ab=\lambda$,then interval for $\lambda$ is

Question

$\begin{array}{1 1}(A)\;(-\infty,4)&(B)\;(-\infty,4)\\(C)\;(4,\infty)&(D)\;(4,\infty)\end{array} $