The correct answer is (b) Nagarjuna.
Nagarjuna was an Indian Buddhist philosopher who lived in the 2nd century CE. He is considered one of the most important figures in the development of Mahayana Buddhism. Nagarjuna is best known for his work on the Madhyamaka philosophy, which argues that all phenomena are empty of inherent existence.
The Milindopanho, also known as the Questions of King Milinda, is a dialogue between the Buddhist monk Nagasena and the Greek king Menander I. The text is a classic of Buddhist literature and is considered an important source of Mahayana doctrine.
Nagsen, Vasubandhu, and Ashwaghosh were all important Indian Buddhist philosophers, but they did not write the Milindopanho. Nagsen was a 1st-century CE philosopher who is considered the founder of the Yogacara school of Mahayana Buddhism. Vasubandhu was a 5th-century CE philosopher who is considered one of the most important figures in the development of the Abhidharma school of Buddhism. Ashwaghosh was a 3rd-century CE poet and philosopher who is considered one of the founders of the Gandharan school of Buddhism.