Concept: Water-borne diseases are caused by pathogens transmitted through contaminated water.
Explanation:Typhoid fever is caused by Salmonella typhi, often spread through contaminated water or food.
Cholera is caused by Vibrio cholerae, also spread mainly through contaminated water.
Gonorrhoea and syphilis are sexually transmitted, not water-borne.
Tuberculosis is usually airborne, not water-borne.
Therefore, the pair that correctly lists water-borne diseases is typhoid and cholera.
Answer: D. typhoid and cholera