Final answer:
The tension generated in a skeletal muscle fiber is directly proportional to the number of sarcomeres, the sites where cross-bridging of actin and myosin generates muscle contraction.
Step-by-step explanation:
The tension generated in a skeletal muscle fiber is directly proportional to the number of cross-bridges formed between actin and myosin within the muscle's sarcomeres. When signaled by a motor neuron, a skeletal muscle fiber contracts, leading to the sarcomere shortening involved in muscle contraction. This process is integral to the sliding filament model of muscle contraction, where the thin filaments slide past the thick ones. Hence, the tension a muscle produces depends on the interactions at the sarcomere level, specifically the cross-bridges that form between actin and myosin. Given this information, the correct answer is option B) Sarcomeres.