The correct answer is: B. Hiuen-tsang.
Hiuen-tsang was a Chinese Buddhist monk who traveled to India in the 7th century CE to study Buddhist scriptures. He is considered one of the most important figures in the transmission of Buddhism to China.
Fa-Hien was a Chinese Buddhist monk who traveled to India in the 5th century CE. He is considered the first Chinese pilgrim to India.
I-tsing was a Chinese Buddhist monk who traveled to India in the 7th century CE. He is considered one of the most important figures in the transmission of Buddhism to China.
Megasthenes was a Greek ambassador to India in the 4th century BCE. He is considered one of the first Europeans to write about India.
Fa-Hien, Hiuen-tsang, and I-tsing were all Buddhist monks who traveled to India in search of Buddhist scriptures. Megasthenes was a Greek ambassador to India who wrote about Indian culture and society.
Hiuen-tsang is considered the most important of these four figures because he was the most prolific writer and the most influential in the transmission of Buddhism to China. He wrote extensively about his travels in India, and his writings are an important source of information about Indian culture and society in the 7th century CE.