A projectile can have the same range 'R' for two angles of projection.If $t_1$ and $t_2$ be the time of flights in the two cases,then the product of the two time of flights is proportional to

Question

$\begin{array}{1 1}R\\\large\frac{1}{R}\\\large\frac{1}{R^2}\\R^2\end{array}$