The question was asked during an interview.
This interesting question is from Transformation of Steel and Cast Iron topic in chapter Constitution of Alloys and Phase Diagrams of Engineering Material & Metallurgy
To explain I would say: The eutectic reaction of cast iron occurs at 1148^oC. Below the eutectic temperature, the cast iron consists of austenite crystals and ledeburite. Cooling of this alloy below 723^oC transforms austenite into pearlite.