Two springs of spring constants $k_1$ and$ k_2$ are joined in series. The effective spring constant of the combination is given by -

Question

( A ) $\frac {K_1K_2} {(K_1+K_2)} $
( B ) $\sqrt{K_1}{K_2}$
( C ) $\frac {(K_1+K_2)}{2}$
( D ) $k1 + k2$