Locus of centriod of the triangle whose vertices are $(a \cos t, a \sin t),(b \sin t,-b \cos t)$ and $(1,0)$ where t is a parameter is

Question

$\begin{array}{1 1}(A)\;(3x+1)^2+(3y)^2=a^2-b^2 \\(B)\;(3x-1)^2+(3y)^2=a^2-b^2 \\(C)\; (3x-1)^2+(3y^2)=a^2+b^2 \\(D)\;(3x+1)^2+(3y)^2=a^2+b^2 \end{array}$