Final answer:
Cardiac muscles are striated, operate involuntarily, and feature intercalated discs that connect cardiomyocytes, ensuring synchronized contractions to pump blood.
Step-by-step explanation:
The correct answer to the question of which features are characteristic of cardiac muscles is C. Striated and involuntary with intercalated discs.
Cardiac muscles are indeed striated, meaning they have the same banded appearance as skeletal muscles due to the organized arrangement of myofibrils into sarcomeres. Unlike skeletal muscles, which are under voluntary control, cardiac muscles operate involuntarily. This means they are controlled by the autonomic nervous system and do not require conscious effort to function. A unique and defining feature of cardiac muscles is the presence of intercalated discs. These specialized structures connect cardiomyocytes (heart muscle cells) end to end, providing mechanical support and electrical connectivity, which allows for the synchronized contraction necessary to pump blood.