A particle is `SHM` is discribed by the displacement function `x(t) = a cos (omegat + theta)` If the initial `(t = 0)` position of the particle `1cm` and its initial velocity is `picm//s` The angular frequency of the particle is `pi rad//s`, then its amplitude is
A. `pi cm`
B. `2cm`
C. `sqrt(2)cm`
D. `1cm`