Final answer:
A plane flying horizontally at a constant speed exhibits linear motion, which is movement in a straight line with constant velocity, different from projectile, circular, or oscillatory motion.
Step-by-step explanation:
A plane flying horizontally at a constant speed above the ground exhibits linear motion. Linear motion refers to the movement in a straight line with a constant velocity, which includes a constant speed and a direct unchanging path. When the conditions of flight are ideal without any turning or vertical movement, and ignoring the curvature of the Earth, the motion of the plane can be considered linear.
It is important to distinguish this from other types of motion. Projectile motion, for example, is the motion of an object thrown or projected into the air, and it is subject to only the acceleration of gravity, typically following a parabolic trajectory. Circular motion, on the other hand, involves an object moving along a curved path such as a circle, and oscillatory motion is seen in objects that move back and forth from a fixed position.
Given the question's details, the correct answer is A) Linear motion, as it best describes a plane flying straight at a constant speed.