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. 1 cm
B. `sqrt2`
C. 2 cm
D. 2.5 cm