Area under a v – t graph represents a physical quantity which has the unit
Area under any x-y Graph will have unit as product of unit of x and unit of y.
That means area under the Graph of velocity and time will have unit equal to Product of unit of velocity (m/s) and unit of time (s).
That would be meter.
For the information, the area under the v-t graph gives displacement.
Hence, the correct option is option B