What is the plug composed of during the clotting response?
platelets and blood plasma
platelets and red blood cells
white blood cells and blood plasma
white blood cells and red blood cells

The plug is composed of platelets and special plasma proteins called fibrin.  The platelets pug is enmeshed in a network of insoluble fibrin molecules.

The aggregation of platelets and formation of fibrin both require the enzyme called thrombin. The clotting process also requires  calcium ions, and about a dozen other protein clotting factors found in plasma.

When blood vessels are cut or damaged, the loss of blood has to be stopped before shock and possible death occur. This is achieved by solidification of blood, a  process called coagulation or clotting.