Muscles have the ability to contract all at one time. a. cardiac (b. skeletal) c. smooth d. none of the above

The correct answer will be option- A.

Explanation:

There are three types of muscles present in the animals: Cardiac, Skeletal and Smooth muscles. These all muscles shows differences in the anatomy and physiology.  

The cardiac muscles are present in the heart which helps in the pumping of the blood to the body. The cardiac muscle are present in the atria and ventricles. Both the atria of the heart contracts when the signals are transferred from the sinoatrial node to the atrioventricular node. These signals lead to the contraction of both atrium at the same time and then of the ventricles at the same time.

Thus, option-A is the correct answer.