The answer is vitamin C. Milady lists each vitamin's specific role in one sentence, and vitamin C is the one it ties directly to skin and tissue repair.
That same sentence gives each of the other choices its own distinct job, which is what makes this a fair multiple-choice question rather than a guess: vitamin A supports overall skin health, vitamin D promotes rapid healing, and vitamin E fights the harmful effects of the sun — all real, but none of them is the one the book names for tissue repair specifically.
Milady Standard Barbering, 6th ed., Ch. 9 (The Skin — Structure, Disorders, and Diseases), p. 240: "Vitamin A supports the overall health of the skin, vitamin C is important to skin and tissue repair, vitamin D promotes healthy and rapid healing of the skin, and vitamin E helps to fight against the harmful effects of the sun."
This is 1 of the real Life Skills questions in FadeJunkie's Milady-sourced 300-question bank. See the Life Skills practice questions page for a fuller sample, or try the Life Skills practice quiz and flashcards for free. A one-time $15 lifetime pass unlocks the complete question bank across all 13 tested topics.
More real Life Skills questions with sourced answers: What Is Called Retailing in a Barbershop, Which Exam Questions Should You Answer First, What Is a Key to Teamwork, What Is the Stem of an Exam Question, and 17 more on the Life Skills practice questions page.
Browse every topic on the Practice Question Hub, or see the Texas Barber State Board Exam Guide for the full exam process — required hours, PSI scheduling, and fees.