Option a is the correct answer. The correct chronological order is as follows: Shankaracharya - 788-820 CE: Shankaracharya was the founder of Advaita Vedanta, a form of Vedanta that advocates non-dualism. Some of his famous works are Brahmasutra Bhashya, Vivekachudamani and Upadesasahasri. Ramanuja - 1017-1137 CE: Ramanuja was the chief proponent of Vishishtadvaita, a form of Vedanta that advocates qualified non-dualism. Some of his famous works are Sri Bhashya, Gita Bhashya and Vedarthasamgraha. Chaitanya - 1486-1534 CE: Chaitanya was the founder of Gaudiya Vaishnavism, a branch of Vaishnavism that worships Krishna as the supreme personality of Godhead. According to this view, Krishna is the source of all other forms of God, including Vishnu and Narayana. Some of his famous works are Shikshashtakam.