When analyzing the motion described by a "kick," it's important to understand the nature of directional changes involved. Among the options provided:
a. A single 90-degree bend indicates a significant, sharp change in direction, forming a right-angle turn.
b. A single change in direction of less than 90 degrees suggests a more subtle and smoother deviation, which is less abrupt than a full right angle.
c. Two equal bends denote two changes in direction that are of the same magnitude but do not necessarily describe a "kick" clearly.
d. A group of three bends implies a series of changes in direction, which makes it more complex and not characteristic of a single "kick".
Considering these choices carefully, the most accurate description of a kick is:
b. A single change in direction of less than 90 degrees.
Hence, the correct answer is:
b: a single change in direction of less than 90 degrees.