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 general and higher education, and business. B2 First is offered in two versions, B2 First for Schools, for school-aged learners, and B2 First, for general and higher education adult learners. B2 First (previously known as the Lower Certificate in English (LCE), First Certificate of English (FCE) and Cambridge English: First) was originally launched in 1939. The arrival of thousands of refugees from the Spanish Civil War and occupied Europe into the UK had created a growing need for language assessment. One hundred and forty-four students sat the first LCE exam on 21 June 1939. The exam was divided into three