Figure shows a system consisting of a massless pulley, a spring of force constant k and a block of mass m. If the block is slightly displaced vertically down from is equilibrium position and then released, the period of its vertical oscillation is
A. `2pisqrt((m)/K)`
B. `pisqrt((m)/(4K)`
C. `pisqrt((m)/(K)`
D. `4pisqrt((m)/(K)`