(d)
Centre and radius of given circle are $( - \lambda,\ 0)$ and
$r = \sqrt{\lambda^{2} - c}$
For limiting, point $r = 0,\ \lambda = \pm \sqrt{c}$
Thus, we get two limiting points of the given coaxial system as $( \pm \sqrt{c},\ 0)$
For real and distinct $c > 0$