text: The<unk>  are eight water-soluble<unk>  that play important roles in cell metabolism.  Historically, the<unk>  were once thought to be a single<unk>  referred to as<unk> B (much like how people refer to<unk> C or<unk> D). Later research showed that they are chemically distinct<unk>  that often coexist in the same foods. Supplements containing all eight<unk>  are generally referred to as a<unk> B complex.  Individual<unk> supplements are referred to by the specific name of each<unk> (e.g. B1, B2, B3).
option_0: B vitamins
option_1: Vitamin A
option_2: Vitamin B6
option_3: Vitamin C
option_4: Thiamin
option_5: Folic acid 
option_6: Cholic acid
option_7: Vitamin D