Final Answer:
An acceleration lane is c. an extra lane at a highway entrance.
Step-by-step explanation:
An acceleration lane is a designated lane at a highway entrance that allows vehicles to increase their speed and smoothly merge with the flow of traffic on the main highway. This additional lane provides drivers with the space needed to accelerate to match the speed of the oncoming traffic before merging into the travel lanes. It enhances safety by facilitating a more gradual and controlled merging process. Options a and b do not accurately describe an acceleration lane, and option d refers to a deceleration or exit lane, not an acceleration lane.
Option C is the answer.