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 B2 First B2 First, previously known as Cambridge English: First and the First Certificate in English (FCE), is an English language examination provided by Cambridge Assessment English (previously known as Cambridge English Language Assessment and University of Cambridge ESOL examinations). B2 First shows that learners have the language skills needed to communicate confidently in an English-speaking environment. It is targeted at Level B2 of the Common European Framework of Reference (CEFR). B2 First is one of the examinations in Cambridge English Qualifications, each of which aligns with a particular level of the CEFR. There are Cambridge English Qualifications for schools,