If $z=2+t+i \sqrt{3-t^{2}}$ where, $t$ is real, the locus of the points $z$ for different values of $t$ is the
(a) circle with centre $(3,0)$ and radius $2 .$
(b) line segment joining the points $(0,1)$ and $(0,-1)$
(c) circle passing through the points $(1,0),(0,1)$ and $(0,-1)$
(d) circle of radius $\sqrt{3}$ passing through $(2-\sqrt{3}, 0)$ and $(2+\sqrt{3}, 0)$.