Which type of muscle works automatically but can sometimes be controlled?

The correct choice is cardiac muscle, not smooth muscle. Cardiac muscle is unique in that it functions automatically, controlling the heartbeat without conscious thought. However, it can also be influenced by the autonomic nervous system, which allows for certain degrees of control during various situations, such as physical exertion, stress, or relaxation.

In contrast, while smooth muscle does also function involuntarily, it lacks the capability for conscious control that cardiac muscle possesses when needed for regulating heart rate. Skeletal muscle, on the other hand, is primarily under voluntary control, allowing for deliberate movements like walking or speaking. Thus, cardiac muscle stands out because it operates largely without conscious control while allowing for some influence through the nervous system in response to different demands on the body.