pendulum $($a$)$: a rod has a mass M and length L;

pendulum $($b$)$: a rod has a mass $2$M and length L;

pendulum $($c$)$: a mass M is attached to a massless string of a length L; and

pendulum $($d$)$: a mass M is attached to a massless string of length $1/2$L$.$

Assume that each pendulum is pulled $22\mathrm{.}7$ to the right and then released. Find the correct period for each pendulum:

A$2$ B$2$ C$2$