Who was appointed as Assembly’s Constitutional Adviser in 1946 during the framing of Indian Constitution?

Who was appointed as Assembly’s Constitutional Adviser in 1946 during the framing of Indian Constitution?
(a) B. N. Rau
(b) B. R. Ammi Ayengar
(c) K.M. Munbedkar
(d) Gopalswashi

Answer – (a) B. N. Rau

B. N. Rau prepared the original draft of the constitution.