Final answer:
Retractors are the instruments used in surgery to hold open layers of tissue, allowing surgeons to access areas beneath the incision site.
Step-by-step explanation:
The instrument that holds open layers of tissue, exposing the areas beneath, is c. Retractors.
Retractors are surgical instruments designed to separate the edges of a surgical incision or wound, or to hold back underlying organs and tissues, so that body parts under the incision may be accessed. They can be hand-held or self-retaining. Unlike the other instruments mentioned, such as hemostats (which are used to stop bleeding by clamping blood vessels), forceps (used to grasp or hold tissues), and towel clamps (used to secure drapes), retractors specifically have the role of maintaining an unobstructed view of, and access to, the surgical site.
In procedures such as arthroscopic surgery, visibility is crucial, and while an endoscope can help illuminate and visualize the area, retractors are still necessary in many surgeries for maintaining exposure.