Answer:
A. City A because there are no pollution sources upstream.
Explanation:
Water pollution is th contamination of water. There are many means through which water is contaminated such as industrial waste, agricultural waste and domestic waste et-cetra.
City A and City B get water from sunset lake and moth lake which have factories (industrial waste) and farmland (agricultural waste) nearby them, which are responsible for the contamination of river water. due to this cities can recieve contaminated water which can affect their health.
But the quality of water in City A will be best than that of City B because according to the image, City A do not have nay upstream soooooource of pollution, as factories and farmland are located at downstream.
Hence, the correct option is A.