State the main function of the respiratory system?

Samuel is a 63-year-old single man who works full time in a food processing plant. he has a history of esophageal cancer, which was treated successfully with anti-cancer drugs and surgery four years ago. his weight had been stable at 135 pounds until 6 months ago. since then, he has experienced an involuntary weight loss of 10 pounds. he complains of a poor appetite and being overly weak, tired, and irritable. he also complains of cracks at the corners of his mouth and a chronic sore throat, which concerns him, given his cancer history. his usual diet is fairly consistent. he states that he rarely eats breakfast because he starts work at 6 a. m. he eats two deli meat sandwiches, "usually pastrami or salami," and a soda at 10 a. m., and may eat a candy bar in the afternoon when he gets off work. he often prepares and eats a frozen dinner or pizza at home in the evening and routinely drinks "about four or five beers" before going to bed. occasionally, he cooks roast and mashed potatoes for dinner and may have cereal with milk for a snack before bed. he rarely eats vegetables or fruit. 1. considering samuel's alcohol consumption, which b vitamin may he be deficient in? a. pantothenic acid b. niacin c. riboflavin d. biotin e. thiamin