3. Rubisco is the most abundant protein on earth and is responsible for fixing carbon dioxide into sugar. Besides carboxylation activity it also possesses oxygenation activity. Which of the following explanations for the persistence of this oxygenase activity is most likely? A. There hasn't been enough time for beneficial mutations to the rubisco gene to arise. B. Because it generates one molecule of phosphoglycerate (PGA) the oxygenation reaction still produces some carbon, so it's not entirely wasteful. C. Oxygenation is an unfortunate trait common to all enzymes that react with carbon dioxide. D. Mutations that have resulted in the loss of oxygenation have resulted in a decrease in carboxylation..