A hole is bored along a diameter of the earth and a particle is dropped into it. If R is the radius of the earth and g is the acceleration due to gravity at the surface of the earth, then the time period of oscillation of the particle is
A. `2pisqrt(R/g)`
B. `2pisqrt((R)/(2g))`
C. `2pisqrt((2R)/(g))`
D. none of these