Final answer:
Exit ramps are the correct answer; they're designed for safe transition from expressways to slower routes. Acceleration lanes, turnpikes, and roundabouts have different traffic management functions.
Step-by-step explanation:
The correct answer to the question "_________ allow you to slow down and leave the expressway" is d) Exit ramps. Exit ramps are specifically designed to help drivers transition from the high speeds of the expressway to the slower speeds required for city driving or to connect to other routes. Unlike acceleration lanes, which are used to increase speed to match that of the expressway, or turnpikes and roundabouts which serve different purposes in traffic management, exit ramps provide a safe and controlled way for vehicles to depart from the main flow of traffic.