Vitamin amino acids. Most vitamins are not single molecules, but groups of related molecules called vitamers. For example, vitamin E consists of four tocopherols and four tocotrienols. The thirteen vitamins required by human metabolism are: vitamin A (retinols and carotenoids), vitamin B (thiamine), vitamin B (riboflavin), vitamin B (niacin), vitamin B (pantothenic acid), vitamin B (pyridoxine), vitamin B (biotin), vitamin B (folic acid or folate), vitamin B (cobalamins), vitamin C (ascorbic acid), vitamin D (calciferols), vitamin E (tocopherols and tocotrienols), and vitamin K (quinones). Vitamins have diverse biochemical functions. Some forms of vitamin A function as regulators of cell and tissue
B2 First European Framework of Reference (CEFR) and is used for study and work purposes. It is an upper-intermediate qualification used to demonstrate that a candidate can use everyday written and spoken English for work and study purposes. A significant number of higher education institutions accept B2 First for admissions or exemption purposes. This includes universities based in: Many companies worldwide accept B2 First as part of their recruitment processes or use it for training and development. These include Deloitte, Ernst & Young, HSBC, Marks & Spencers, and Nestlé. B2 First B2 First, previously known as Cambridge English: First and the First