Ans. is 'd' i.e., Water sanitationControl of cholera (WHO guidelines)o Measures taken to control cholera epidemic are1) Verification of diagnosis: Identification of V. cholera 01 in stools of few patients is sufficient. It is not necessary to culture stools of all cases or contacts.2) Notification: Cholera is notifiable disease locally, nationally and internationally. Under the International health Regulations, cholera is notifiable to WHO within 24 hours of its occurrence by national government. An area is declared free of cholera when twice the incubation period (i.e., 10 days) has elapsed since the death, recovery or isolation of the last case.3) Early case finding4) Establishment of treatment centers.5) Rehydration therapy: Oral (ORS) or intravenous.6) Adjunct to therapy: Antibiotic should be given as soon as vomiting has stoped. Doxycyclone (tetracycline) in single dose is the treatment of choice in adults. In children, cotrimoxazole is the drug of choice. Furazolidine is preferred in pregnant females.7) Epidemiological investigation: Epidemiological studies.8) Sanitation measures: As water is the most important vehicle, provision of safe water (chlorination or boiling) is most important. Other important measures are proper excreta disposal, food sanitation and disinfection of stools/vomits/clothes etc by cresol.9) Chemoprophylaxis: Chemoprophylaxis to close contact is indicated. Mass chemoprophylaxis is not advised. Drug of choice is tetracycline.10) Vaccination: They are of no value in controlling epidemic.11) Health education: The most effective prophylactic measure.