The correct option is 1, 2, and 3 because all three groups—Cnidarians, Fungi, and Protozoa—can engage in symbiotic relationships with other organisms. Cnidarians, such as corals, often form mutualistic associations with zooxanthellae, which provides them with nutrients through photosynthesis. Fungi form critical symbiotic networks with plants (mycorrhizae) and other organisms, facilitating nutrient exchange, while protozoa can host endosymbiotic bacteria and form relationships with other organisms, contributing to various ecological processes. Understanding these relationships highlights the interconnectedness of ecosystems, a crucial aspect of biological and ecological studies in UPSC examinations.