Suppose $a, b, c$ are in A.P. and $a^{2}, b^{2}, c^{2}$ are in G.P. If $a<b<c$ and $a+b+c=\frac{3}{2}$, then the value of $a$ is
(A) $\frac{1}{2 \sqrt{2}}$
(B) $\frac{1}{2 \sqrt{3}}$
(C) $\frac{1}{2}-\frac{1}{\sqrt{3}}$
(D) $\frac{1}{2}-\frac{1}{\sqrt{2}}$