Let $S _ { 1 } : x ^ { 2 } + y ^ { 2 } = 9$ and $S _ { 2 } : ( x - 2 ) ^ { 2 } + y ^ { 2 } = 1$.
Then the locus of center of a variable circle $S$ which touches $S _ { 1 }$ internally and $S _ { 2 }$ externally always passes through the points:\\
(1) $( 0 , \pm \sqrt { 3 } )$\\
(2) $\left( \frac { 1 } { 2 } , \pm \frac { \sqrt { 5 } } { 2 } \right)$\\
(3) $\left( 2 , \pm \frac { 3 } { 2 } \right)$\\
(4) $( 1 , \pm 2 )$