A neutron of mass m is confined within a nucleus of diameter d. Ignoring numerical constants, what is an approximate expression for the kinetic energy of the neutron?

A.  \(\frac{{{h^2}}}{{m{d^2}}}\)

B.  \(\frac{h}{{md}}\)

C.  \(\frac{{m{h^2}}}{{{d^2}}}\)

D.  \(\frac{h}{{{m^2}d}}\)

A