D. It [the golf ball] will travel in a straight path unless changed by an external force. The 1s Law of Motion states, "Every object will remain at rest or in uniform motion in a straight line unless compelled to change its state by the action of an external force." The behavior of all objects can be described by saying that objects tend to "keep on doing what they're doing" (unless acted upon by an unbalanced force). If at rest, they will continue in this same state of rest. If in motion with an eastward velocity of 5 m/s for example, they will continue in this same state of motion (5 m/s, East). If in motion with a leftward velocity of 2 m/s, they will continue in this same state of motion (2 m/s, left). The state of motion of an object is maintained as long as the object is not acted upon by an unbalanced force. All objects resist changes in their state of motion - they tend to "keep on doing what they're doing." The choice of "D" simply restates this. Choice "A" is based upon Newton's 3rd Law of Motion. Choices "B" and "C" are based upon Newton's 2nd Law of Motion.