A particles is SHM is described by the displacement function `x(t)= a cos (omegat+theta).` If the initinal `(t=0)` position of the particle is 1 cm and its initinal velcotiy is `pi cm//s.` The angular frequncy of the particle is `pi rad//s`. Then is amplitude is
A. 1 cm
B. `sqrt2 cm `
C. `2 cm`
D. `2.5 cm`