The speed of a particle executing motion changes with time according to the equation $\mathrm{y}=\mathrm{a} \sin \omega \mathrm{t}+\mathrm{b} \cos \omega \mathrm{t}$, then $\ldots \ldots \ldots$
(A) Motion is periodic but not a S.H.M.
(B) It is a S.H.M. with amplitude equal to $\mathrm{a}+\mathrm{b}$
(C) It is a S.H.M. with amplitude equal to $\mathrm{a}^{2}+\mathrm{b}^{2}$