In this section, each item consists of six sentences of a passage. The first and sixth sentences are given as SI and S6. The middle four sentences in each have been jumbled up and labelled as P, Q, R and S. You are required to find the proper sequence of the four sentences and mark your response accordingly.

S1: You must have heard about Qutub Minar.
P:  The iron pillar near the Qutub Minar in Delhi was built more than 1600 years ago by the ironworkers of India. 
Q: For its quality of rust resistance, it has been examined by scientists from all parts of the world. 
R: They had developed a process which prevented iron from rusting.
S: The iron pillar is 8 m high and weighs 6 tonnes (6000 kg). 
S6: That is why it is very heavy.