A mechanism is best defined as:

• A. A machine or device
• B. The working parts of a machine
• C. A process or system by which something occurs
• D. A type of lever

Answer: (A)

Mechanism refers to a system where parts work together to produce a specific effect, typically by transferring or transforming energy into motion. In practical terms, it’s essentially a machine or device—the tangible object designed to perform a function. That’s why this option fits best: it directly captures the idea of a device whose components are arranged to make something happen. The idea of the “working parts” is related but narrower, focusing on components rather than the whole system. A “process or system by which something occurs” describes a method rather than the physical mechanism, and a “type of lever” is just one example, not the general concept.