This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Vitamins, Subject name: Social & Preventive Medicine
According to prevalence criteria for determining xerophthalmia problems given by WHO, following are true for an endemic area: 
Select and explain. 
A. Bitot spot 5% poluation of under 6 yrs, B. Conjuctival xerosis 1%, C. Conjuctival ulcers 0.05%, D. Night blindness 1%
D: Night blindness 1%
Answer: D: Night blindness 1% 
Explanation: Ans. (d) Night blindness 1%Ref : K. Park 23rd ed. / 615, 641, 899Criteria and Prevalence for Determining Xerophthalmia Severity:CriteriaPrevalence at risk* Night blindness>1%* Bitot's spot>0.5%* Corneal xerosis/keratomalacia>0.01%* Corneal ulcer>0.05%* Serum retinol>5%* Refer to previous answer for WHO classification of Xerophthalmia