Помогите с упражнением по английскому.

1. The number of cells varies in different parts of the body. (Active Voice)
2. Pigment melanin is produced by special cells in the epidermis. (Passive Voice)
3. Cells were discovered in the middle of the seventeenth century. (Passive Voice)
4. The smallest arteries branch into numerous tiny capillaries. (Active Voice)
5. The entire bony system is pierced throughout by a rich network of vessels. (Passive Voice)
6. Nervous system connects the brain to the rest of the body through nerves. (Active Voice)
7. Most of the space in the upper right abdomen is taken up by the liver. (Passive Voice)
8. The development of the skeleton and its eventual size and density is influenced by the genetic factors. (Passive Voice)
9. In the small intestine, the process of digestion completes action of the bile. (Active Voice)
10. In recent times, genetic engineering has increasingly been used in the field of biotechnology. (Passive Voice)
11. Most vitamins are required only in extremely small amounts, and each vitamin is presented in many different foods. (Passive Voice)
12. Some vitamins occur in inactive forms that do not influence chemical reactions. (Active Voice)
13. In vitamin A deficiency, the epithelial tissues of many organs are affected. (Passive Voice)
14. Vitamin B deficiency is accompanied by poor growth, dermatitis, anemia, kidney and adrenal lesions. (Passive Voice)
15. Several coenzymes of vitamin B12 exist. (Active Voice)
16. Little is known of the metabolic role of vitamin D. (Passive Voice)
17. The body requires only small amounts of vitamin D which is provided by a balanced diet and normal exposure to sunlight. (Active Voice) / (Passive Voice)
18. Intestinal bacteria manufacture vitamin K in the body, and so deficiencies of this vitamin rarely are resulted from a poor diet. (Active Voice) / (Passive Voice)