Final answer:
The correct answer to the student's question is 'A. actin and myosin sliding past each other and partially overlapping', which describes the mechanism of muscle contraction according to the sliding filament model.
Step-by-step explanation:
The sliding filament model of contraction describes the process by which muscle cells contract. The key to this model is that the sarcomere, the fundamental unit of muscle contraction, shortens as the thick (myosin) and thin (actin) filaments slide past each other without changing their own lengths. This sliding enables the sarcomeres to shorten, which leads to the overall shortening and contraction of the muscle fiber. During this process, the myosin heads bind to actin forming cross-bridges, and as they pull on the actin filaments, the sarcomere shortens. According to the options given, the correct answer would be 'A. actin and myosin sliding past each other and partially overlapping', as the other options incorrectly describe the mechanism of muscle contraction dictated by the sliding filament model.