Option (a) is incorrect. Cardiac muscles are present in the heart. They are involuntary muscles since their contraction does not depend on the will of an individual. Cardiac muscles are composed of cardiomyocytes present on the walls of the heart. Though cardiac muscles are involuntary muscles, they are structurally related to the skeletal or voluntary muscles. The cardiomyocytes contain only one nucleus, but they are functionally syncytium, that is each cardiomyocyte works in a coordinated manner with the next cell to pump blood efficiently. The cardiomyocytes are connected to each other with the help of intercalated discs. Thus, cardiac muscles are not multinucleated and true syncytium but appear to be so.
Option (b) is incorrect. Smooth muscles are involuntary muscles. They are present in the esophagus, stomach, urinary bladder and uterus. Their movement is not under the control of an individual’s will. Smooth muscles lack striations and are therefore called non-striated muscles. The smooth muscles have an elongated structure with pointed ends. They contain only one nucleus and are called uninucleate structures.
Option (c) is correct. Voluntary muscles are skeletal muscles. The movement of skeletal muscles is under the will of one’s will. Skeletal muscles are composed of myofibrils, which in turn are composed of repeated units called sarcomeres. The skeletal muscles are formed by a process of myogenesis by the fusion of several uninucleate cells. Skeletal muscles are therefore multinucleate entities. Skeletal muscles are found attached to the bones. They help in the movement of body parts, protect the internal organs and maintain body shape.