$\Delta ABC$ $\tan \frac{A}{2},\tan \frac{B}{2},\tan \frac{C}{2}$ in A.P.Then ${\sin ^2}\frac{A}{2},{\sin ^2}\frac{B}{2},{\sin ^2}\frac{C}{2}$ are in:

a) A.P.
b) G.P.
c) H.P.

d) None of the options given