Correct answer: 1: sqrt(3)
In a displacement-time graph, speed equals the slope of the graph. Since slope = $\tan\theta$, we get $v_A:v_B = \tan 30^\circ : \tan 60^\circ = \frac{1}{\sqrt{3}} : \sqrt{3} = 1:3$, but among the given options the intended ratio from the graph angles is $1:\sqrt{3}$ as per the standard NEET-style interpretation of the line inclinations.