Correct Answer: (a) they are Indian research reactor.
Solution:Dhruva, Purnima, and Cirus are Indian research reactors. Purnima - I, II and III were indigenously designed reactors. All of these 3 reactors were decommissioned decades ago. Cirus was a heavy water tank reactor, fuelled with 10 tons of natural uranium and generating about 40 Megawatts of thermal power. It was supplied by Canada and became fully operational in 1960. This reactor was permanently shutdown in 2010. While Dhruva is a heavy water tank reactor, fuelled with 6.5 tons of natural uranium indigenously supplied, and generating 100 MW of power.