The correct option is D Ribulose-1, 5-biphosphate
The primary carbon dioxide acceptor in the dark reaction is Ribulose 1,5 bisphosphate or RUBP, which is carboxylated by the enzyme Ribulose 1,5 bisphosphate carboxylase oxygenase or RuBisCo. As a result of this carboxylation, two molecules of three carbon atom compound phosphoglyceric acid are produced as the first stable product of C3 cycle.