An open drain system is a breeding place for all of these (flies, mosquitoes, and organisms which cause diseases).
Explanation: Stagnant water in open drains provides a suitable environment for the development of various insects like flies and mosquitoes, and it can also harbor bacteria and other microorganisms that can cause diseases.
Key points:
Flies and mosquitoes: These insects commonly breed in stagnant water found in open drains.
Disease-causing organisms: Bacteria and other microbes can thrive in open drains, potentially contaminating the water and surrounding area.