The correct option is A Both A and R are true and R is the correct explanation of A.
Bose went to England to appear for the Indian Civil Service exam. He passed the exam and stood fourth on the merit list. However, when he heard about the Jallianwala Bagh massacre, he was disturbed by the British action in India and was unable to complete his probation period. He decided to resign from his service and followed Gandhi's call of Non-Cooperation against the British. Leaving behind everything, he came to India, and in 1921 he joined politics.