The correct answer is B. Kanishka I.
Kanishka I was the greatest Kushana ruler whose contribution to Buddhism was even greater than that of Ashoka. He was a great patron of Buddhism and convened the Fourth Buddhist Council at Kundalvana in Kashmir. He also built many Buddhist monasteries and stupas, and spread Buddhism to Central Asia and China.
Kadphises was the founder of the Kushan Empire. He was a great conqueror, but he did not contribute much to Buddhism.
Vasishka was the successor of Kanishka I. He was also a great patron of Buddhism, but his contributions were not as great as those of Kanishka I.
Huvishka was the successor of Vasishka. He was also a great patron of Buddhism, but his contributions were not as great as those of Kanishka I or Vasishka.
Kanishka I was the greatest Kushana ruler whose contribution to Buddhism was even greater than that of Ashoka. He was a great patron of Buddhism and convened the Fourth Buddhist Council at Kundalvana in Kashmir. He also built many Buddhist monasteries and stupas, and spread Buddhism to Central Asia and China.