Correct Option: A

The Idukki Hydroelectric Project is the biggest hydroelectric Project in Kerala (India). It comprises of three dams at Idukki, Cheruthony and Kulamavu and related systems. The powerhouse at Moolamattom is the longest underground power station in India and the pressure shaft is the largest in the country. The Idukki dam is one of the highest dams in the world and the first arch dam in India. Cheruthony is the largest and highest gravity dam in Kerala.