$A$ body of mass $m$ connected to a massless and unstretchable string moves in a vertical circle of radius $R$ under gravity $g$. The other end of the string is fixed at the center of the circle. If the velocity at the top of the circular path is $n\sqrt{gR}$,where $n \geq 1$,then the ratio of the kinetic energy of the body at the bottom to that at the top of the circle is:

• A
  $\frac{n}{n+4}$
• B
  $\frac{n+4}{n}$
• C
  $\frac{n^2}{n^2+4}$
• D
  $\frac{n^2+4}{n^2}$