Acceleration versus time graphs for four objects are shown below. All axes have the same scale. Which object had the greatest change in velocity during the interval?

In option (b) area of graph is $\frac{1}{2}{\mathrm{t}}_{\mathrm{o}}{\mathrm{a}}_{\mathrm{o}}. \mathrm{But} \mathrm{in} \mathrm{option} \left(\mathrm{a}\right) \mathrm{and} \left(\mathrm{c}\right) \mathrm{area} \mathrm{is} \mathrm{less} \mathrm{than} \frac{1}{2}{\mathrm{t}}_{\mathrm{o}}{\mathrm{a}}_{\mathrm{o}}. \mathrm{In} \mathrm{option} \left(\mathrm{d}\right), \mathrm{area} \mathrm{is} \mathrm{more} \mathrm{than} \frac{1}{2}{\mathrm{t}}_{\mathrm{o}}{\mathrm{a}}_{\mathrm{o}}. \mathrm{So} \mathrm{in} \mathrm{option} \left(\mathrm{d}\right) \mathrm{change} \mathrm{in} \mathrm{velocity} \mathrm{is} \mathrm{greatest}.$