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: Science has given us powers fit for the gods.
P: For example, we do not know how to manage our machines. 
Q: Yet we use them like small children.
​R: But in practice, they have become man's masters. 
S: Machines were made to be man's servants. 
S6: And we should remember that they are very stern masters.