Bhakti cult was popularized by Chaitanya Mahaprabhu in Bengal who was a devotee of:
A. Lord Krishna
B. Lord Rama
C. Lord Shiva
D. Lord Ganesh

Hint: The founder of Achintya Bedha Abedha (a school of Vedanta philosophy), this 1$5^{th}$-century saint was considered a reincarnation of Lord Krishna by some devotees. He propagated Bhakti yoga.

Complete answer: Option A. His practices have drastically influenced the evolution of Vaishnavism in Bengal. His birth name was Vishwambhar Mishra, but he was also called Gaura (golden or fair-skinned) and Nimal (because he was born under a neem tree). Lord Krishna is a major deity, who is worshipped as the $8^{th}$ avatar of Vishnu.
Option B. He is the protagonist of the epic Ramayana. He is the $7^{th}$ avatar of Vishnu. Famous festivals revolving around him include Ram Navami and Diwali. This is, however, an incorrect option.
Option C. He forms one of the holy trinity in Hinduism and plays the role of the destroyer. The other two are Brahma and Vishnu. He is also revered as the ‘Mahadeva’. Hence, this is the wrong option.
Option D. He is the elephant-headed God and is worshipped at the start of anything auspicious. This is not the right option though. The festival dedicated to him is 10 days long and is called Ganesh Chaturthi.
Therefore, option A is the correct answer.

Note: The Bhakti movement gave birth to Sikhism. Buddhism and Jainism also gained popularity. It gave regional deities visibility, and reformed the approach to religion, by emphasizing on spirituality over rigid rituals.