The particle has a constant acceleration because the slope of the curve is constant.
This option is not necessarily true based solely on a straight line on the velocity-time plot. A straight line indicates constant velocity or constant acceleration, but it doesn't provide information about whether the particle has turned around.
This option is not necessarily true. A straight line on the velocity-time plot could represent a particle moving at a constant velocity in one direction, which would result in non-zero displacement.
This option is not necessarily true. A straight line on the velocity-time plot provides information about the particle's motion, but it may not provide a complete picture of the motion.
The correct statement is A. The particle has a constant acceleration. A straight line on a velocity-time plot typically indicates that the particle is undergoing constant acceleration.