A weightless rod is acted on by upward parallel forces of `2 N` and `4N` ends `A` and `B` respectively. The total length of the rod `AB=3m`. To keep the rod in equilibrium a fo rce of `6 N` should act in the following manner :
A. Downwards at any point between `A` and `B`
B. Downwards at the mid point of `AB`
C. Downwards at a point `C` such that `AC = 1 m`
D. Downwards at a point `D` such that `BD = 1 m`.