Correct matching is (A)-(I), (B)-(IV), (C)-(II), (D)-(III):

• Ergocalciferol: Plant- and fungal-derived form known as Vitamin D2 (I).
• Cholecalciferol: Animal form synthesized photochemically in skin from 7-dehydrocholesterol, known as Vitamin D3 (IV).
• Calcidiol: 25-hydroxyvitamin D3 [25(OH)D3], the major circulating storage form synthesized in the liver (II).
• Calcitriol: 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], the biologically active hormonal form produced in the kidneys via 1-alpha-hydroxylase (III).

Both (A) and (R) are true and (R) is the correct explanation of (A). Most animals synthesize L-ascorbic acid from D-glucose via the glucuronic acid pathway. In primates (including humans), guinea pigs, and teleost fishes, the terminal enzyme L-gulonolactone oxidase (GLO, encoded by the GULO gene) accumulated deleterious mutations during evolutionary divergence, turning it into an inactive pseudogene. As a consequence, humans completely lost the endogenous capacity for ascorbic acid synthesis and became strictly dependent on dietary vitamin C.

Statements (A), (B), and (D) only are correct:

• Rubisco activase (RCA) is a specialized catalytic AAA+ molecular chaperone (A) that couples the energy of ATP hydrolysis (B) to induce conformational remodeling of Rubisco.
• By remodeling the active site, RCA dislodges tightly bound inhibitory sugar phosphates (such as uncarbamylated RuBP, xylulose-1,5-bisphosphate, or CA1P) from the catalytic pocket (making C false).
• The release of these inhibitors exposes the essential active-site lysine residue (Lys-201), permitting its activational carbamylation by an activator CO2 molecule and coordination with Mg2+ (D).