The correct option is A Collagen
Collagen is the most abundant protein in the animal world and also in the human body. It is found in bones, muscles, skin and tendons. It provides strength and structure to the body.
It is involved in ageing. As the age advances, collagen becomes rigid and impermeable to water and nutrients due to which they find it difficult to move into cells. Also, waste byproducts formed inside the cells find it difficult to move out of the cells.
RuBisCO is known as Ribulose bisphosphate carboxylase oxygenase and is the most abundant protein in nature. It is an enzyme involved in photosynthesis.
Serum albumin is found in the blood and hence also known as blood albumin. It is the most abundant protein in human blood. It is synthesized in the liver, is monomeric and water soluble.
Prothrombin is a protein synthesized in the liver. It is required in blood clotting.