The correct option is B AB
We know that, slope of s−t graph gives speed.
In position AB the graph is parallel to t - axis.
∴ slope is equal to zero.
Thus, the speed of the particle is zero.
Along OA, the speed of the particle is constant as slope is constant.
Along BC, the speed of the particle is constant as slope is constant.
Hence, option (b) is the correct alternative.