Option a is the correct answer. Bhakti Saints played a significant role in spreading their devotional teachings to the masses. To ensure their message reached a broader audience and had a profound impact on people, they composed their devotional verses, songs, and sermons in the languages understood by the common people. The Bhakti Saints were poets and singers who expressed their devotion to God in various local languages, such as Tamil, Telugu, Kannada, Hindi, Bengali, Marathi, Gujarati, etc. They used simple and popular forms of literature, such as dohas, padas, abhangas, vachanas, etc. Option b is incorrect: Bhakti saints like Chaitanya Mahaprabhu and Sant Tukaram did not reject the authority of priestly classes. Option c is incorrect: Shankaracharya and Madhvacharya considered women inferior to men and discouraged their temple entry. Option d is incorrect: Some of them encouraged idol worship, but not all of them. For example, Kabir was against idolatry and believed in a formless God who could be reached through love and service.