Part B will come first as it mentions that in Dr. Babasaheb Ambedkar, we get to see a crusader against a caste system. Part A follows and implies that not only a crusader but we can also see an elder statesman and a national leader in him. Part C further follows and mentions what all can be seen him. Part D preceded S6 and the pair D-S6 mentions that his contributions will be cherished forever.
The correct sentence is: In Dr. Babasaheb Ambedkar, we have not only a crusader against the caste system, but also an elder statesman and national leader, a valiant fighter for the cause of the downtrodden in India, whose contribution in the form of the Constitution of India will be cherished forever by posterity.
So, the correct order is BACD.
Hence, option (c) is the answer.