The link to the two questions :
The v-t graph has two sections.
The first section is a horizontal line, which means constant non-zero speed. This corresponds to inclined strainght-line segment on the x-t graph. The second section is an inclined strainght-line segment, which means that the speed is increasing at a constant rate. This corresponds to parabolic curve on x-t graph.
Taking into account the facts listed above, the correct answer option is C.