APA
World Health Organization, . (1997). Vitamin a supplement: a guide to their use in the treament and prevention of vitamin a deficiency and xerophthalmia. Geneva: World Health Oraganization.
Chicago
World Health Organization, . 1997. Vitamin a supplement: a guide to their use in the treament and prevention of vitamin a deficiency and xerophthalmia. Geneva: World Health Oraganization.
Harvard
World Health Organization, . (1997). Vitamin a supplement: a guide to their use in the treament and prevention of vitamin a deficiency and xerophthalmia. Geneva: World Health Oraganization.
MLA
World Health Organization, . Vitamin a supplement: a guide to their use in the treament and prevention of vitamin a deficiency and xerophthalmia. Geneva: World Health Oraganization. 1997.