B.R. Ambedkar attended all three Round Table Conferences. The Round Table Conferences were a series of discussions held in the 1930s to consider and discuss constitutional reforms in India. B.R. Ambedkar, a key figure in the drafting of the Indian Constitution and a champion of the rights of the Dalit community, actively participated in these conferences.

The policy of imperial preferences adopted by Britain in its colonies in 1932 is also known as the Ottawa Agreement. This agreement was a series of bilateral trade agreements between the United Kingdom and various members of the British Empire, including Canada, Australia, South Africa, and New Zealand. The agreements aimed to promote trade within the British Empire by providing preferential treatment to goods from member countries.

Answer: A) 1954 Explanation: The Bharat Ratna is the highest civilian award of the Republic of India. Instituted in 1954, the award is conferred "in recognition of exceptional service/performance of the highest order", without distinction of race, occupation, position, or sex.