Final answer:
The accessory protein that stabilizes actin filaments and prevents the interaction between actin and myosin in relaxed muscle is tropomyosin, which is covered by calcium ions during muscle contraction to allow binding.
Step-by-step explanation:
The accessory protein that stabilizes actin filaments and prevents actin from binding to myosin in relaxed muscles is tropomyosin. Tropomyosin winds around the actin filaments and covers the myosin-binding sites. This function is integral to the regulation of muscle contraction, as it ensures actin and myosin binding occurs only when the muscle is signaled to contract.
In summary, a) Tropomyosin is the correct answer to the question about the accessory protein that stabilizes actin filaments. Other proteins mentioned, like Profilin and CapZ, play different roles in the actin filament dynamics, whereas myosin is the motor protein that interacts with actin to generate muscle contraction.