The potential functions of gears are: changes in direction, speed changes (both increases and decreases), and motion transmission.
Gears possess multiple functions, including speed and direction changes and motion transmission. For this reason, the response involving three gear uses is the only correct answer.
B Gears possess a single function: transmitting motion.
C Gears are primarily used for making changes in speed, but may also be used to instigate motion in machinery.
D Gears may be used to change direction in machinery and can be used to increase speed.