The correct answer is B. Bimbisara.
Bimbisara was the king of Magadha from 544 to 491 BCE. He was a contemporary of both Vardhaman Mahavira and the Buddha. Mahavira was the founder of Jainism, and the Buddha was the founder of Buddhism. Both men preached their doctrines during Bimbisara’s reign.
Ajatashatru was the son of Bimbisara. He succeeded his father as king of Magadha in 491 BCE. Ajatashatru was a powerful ruler who expanded the kingdom of Magadha. He is also known for his conflict with the Buddha.
Udayin was the son of Ajatashatru. He succeeded his father as king of Magadha in 461 BCE. Udayin was a popular ruler who is known for his patronage of the arts.
Harshavardhana was the king of the Gupta Empire from 606 to 647 CE. He was a powerful ruler who reunited much of the Indian subcontinent under his rule. Harshavardhana is also known for his patronage of the arts and literature.
Bimbisara was the only ruler among the four who was a contemporary of both Vardhaman Mahavira and the Buddha. Therefore, he is the correct answer to the question.