In the following items, each passage consists of six sentences. The first sentence (S1) and the final sentence (S6) are given. The middle four sentences in each have been removed and jumbled up. These are labelled P, Q, R and S. You are required to find out the proper sequence of the four sentences and mark accordingly on the Answer Sheet. 

S1: Stalin sent General Zhukov to assume command in Leningrad. 
P: True, the city was prepared for street fighting. 
Q: At that time no one knew whether the city could be saved. 
​R: No one knew the answer. 
S: But would the city's defences hold?
S6: The battle for Leningrad was the fiercest ever fought.