The correct option is D semi circular arc
The velocity-time graph for a body with non-uniform motion is a curve.
Hence semi circular arc is the correct option. The body travels different distances in equal intervals of time, hence its velocity also changes by different amounts in equal intervals of time.
While y=10 is a hypothetical case, when velocity is becoming infinite in short interval of time. Such case is not possible.
For the case of line parallel to x axis, then such case is that of constant velocity.