Which one of the following is the most abundant protein in the animals?

Collagen is the most abundant protein in the animal world. This is one of the main components of our connective tissue and are associated with bones, cartilages, tendons, skin etc. It is the substance that holds the body together. Collagen forms a scaffold to provide strength and structure. 

RuBisCO is the most abundant protein in the whole of the biosphere. RuBisCO is an enzyme involved in carbon fixation (photosynthesis), a process by which the atmospheric CO₂ is converted by plants to energy rich molecules i.e. glucose.