Two important hydrogen carriers, NAD (nicotinamide adenine dinucleotide) and FAD (flavin adenine dinucleotide), act as co-enzymes. They are derived from the vitamins ________ and ________.
a) Vitamin A and Vitamin C
b) Vitamin B₁₂ and Vitamin D
c) Vitamin B₆ and Vitamin E
d) Vitamin B₃ and Vitamin B₂