A. Thicker but longer than actin filaments
Reason: The thick filament consists mainly of myosin protein. Myosin contributes 55 percent of muscle protein by weight and found only in A-band of sarcomere. The myosin molecule is composed of six polypeptide chains, two identical heavy chains and four light chains. Myosin consists of two proteins, myosin and meromysin. Myosin thicker but longer than actin filaments. In actin filaments, found in both A and I-bands. It consists of three proteins, actin, tropomyosin and troponin. It thinner but shorter than myosin filaments.