The correct answer is option 'B', i.e., Mahayana sect.

Explanation:
Gandhara School of Art is a style of Buddhist visual art that developed in what is now northwestern Pakistan and eastern Afghanistan, between the 1st century BCE and the 7th century CE, under the Kushan Empire and Greco-Buddhist kingdoms. The Gandhara School of Art was the first style of Buddhist art to develop in the Indian subcontinent and was heavily influenced by the Hellenistic art of the Greek kingdoms in Central Asia.

The Gandhara School of Art developed in the Mahayana sect of Buddhism, which was prevalent in the region during that time. The Mahayana sect is one of the two major traditions of Buddhism, the other being Theravada. Mahayana Buddhism developed in the first century BCE, and its followers sought to create a more accessible form of Buddhism that could appeal to a broader audience.

The Gandhara School of Art was characterized by a fusion of Indian and Hellenistic styles, with a focus on naturalism and realism. The artists of the Gandhara School used a variety of materials, including stone, stucco, and bronze, to create images of the Buddha and other Buddhist figures. They also created narrative scenes from the life of the Buddha and other important events in Buddhist history.

In conclusion, the Gandhara School of Art developed in the Mahayana sect of Buddhism, which was prevalent in the region during that time. It was characterized by a fusion of Indian and Hellenistic styles and was the first style of Buddhist art to develop in the Indian subcontinent.