Final answer:
India and Pakistan became the first new members of the British Commonwealth since 1931.
Step-by-step explanation:
The two nations that became the first new members of the British Commonwealth since the original group in 1931 were India and Pakistan (option a).
After gaining independence in 1947, India and Pakistan were granted membership in the British Commonwealth. This was a significant development as it marked the inclusion of two newly independent nations into the Commonwealth.
The partition of India in 1947 led to the creation of Pakistan, which became a separate Muslim-majority nation. Both India and Pakistan have remained members of the Commonwealth, with India becoming the largest member country and Pakistan playing an active role within the organization.