In the question below, the passage consists of six sentences. The first and sixth sentences (S1 and S6) are given in the beginning and at the end respectively. The middle four sentences have been removed and jumbled up. These are labeled as A, B, C and D. Find out the proper order for the four sentences. S1: Calcutta unlike other cities kept its trams. A: As a result there horrendous congestion. B: It was going to be the first in South Asia. C: They run down the center of the road D: To ease in the city decided to build an underground railway line S6: The foundation stone was laid in 1972 The Proper sequence should be :