The path of a particle moving under the influence of a force fixed in magnitude and direction is

The correct option is A

Straight line

The explanation for the correct option:

In the case of option A,

1. The path traced by a moving particle is called a trajectory.
2. Since the force's direction doesn't change so the particle's velocity stays constant.
3. So there is no acceleration.
4. Thus, the path of a particle moving under the influence of a force fixed in magnitude and direction will be a straight line

The explanation for the incorrect option:

In the case of option B,

1. For a particle to move in a circular path it is required to have a change in the direction of the position vector.
2. Here the direction is not changing.
3. Thus it can not be in a circular motion.

In the case of option C,

1. For a particle to be in parabolic motion it is needed that the particle or body is projected at an angle.
2. For instance, a rocket launch follows a projectile path.

In the case of option D,

1. Elliptical motion is carried out by a particle having angular acceleration.
2. For instance, our planets follow the elliptical path.

Hence option A is the correct answer.