The maximum tension a rope can withstand is $6\;kg$ wt. The ratio of maximum acceleration with two boys of masses $20\; kg$ can climb up rope at the same time is :

Question

$$\begin {array} {1 1} (a)\;1:2 & \quad (b)\;2:1 \\ (c)\;4:3 & \quad (d)\;3:2 \end {array}$$