The correct answer is option 3: normal activity of sex glands. Vitamin E plays a crucial role in the proper functioning of the sex glands, which includes the production of hormones and the maintenance of reproductive health. It is essential for both male and female sexual health. Vitamin E also acts as an antioxidant, protecting the cells from damage caused by free radicals.

Option 1, development of teeth, is incorrect because Vitamin E does not directly impact tooth development. Option 2, carbohydrate metabolism, is incorrect because the primary nutrient involved in carbohydrate metabolism is Vitamin B. Option 4, general health of epithelial tissues, is also incorrect because Vitamin E primarily supports the functioning of sex glands rather than epithelial tissues.