The correct option is B RuBP carboxylase
Ribulose-1,5-bisphosphate carboxylase/oxygenase, commonly known by the abbreviation RuBisCO, is an enzyme involved in the first major step of carbon fixation, a process by which atmospheric carbon dioxide is converted by plants to energy-rich molecules such as glucose during the dark reaction in the stroma. In chemical terms, it catalyzes the carboxylation of ribulose-1,5-bisphosphate (also known as RuBP). It is probably the most abundant protein on Earth compared to other proteins such as dehydrogenase, pyruvic carbohydrates and hexokinase. Thus, the correct answer is option B.