Option a is the correct answer. The Barabar caves are a group of rock-cut caves located in the Jehanabad district of Bihar, India. They were built by the Mauryan emperor Ashoka in the 3rd century BCE. The caves are dedicated to the Ajivikas, a sect of Indian ascetics who flourished in the 6th and 5th centuries BCE. The caves are carved out of sandstone hills and are simple in design. They consist of a single chamber with a square or rectangular plan. The caves are decorated with pillars and pilasters, and some of them have inscriptions.