In the following question, there are six sentences marked S1, S6, P, Q, R and…

Correct sequence (full passage): We do not know how to manage our machines. Machines were made to be man's servants, yet he has grown so dependent on them that they are in a fair way to become his masters. Already most men spend most of their lives looking after and waiting upon machines. The machines are very stern masters. They must be fed with coal, and given petrol to drink, and oil to wash with, and must be kept at the right temperature. If they do not get their meals when they expect them, they grow sulky and refuse to work.

Explanation:

• 1) The opening sentence "We do not know how to manage our machines" sets the problem and is naturally followed by the sentence explaining that machines, though made to be servants, have begun to dominate us — this gives a general diagnosis of the problem.

• 2) The sentence that says most men spend their lives looking after machines provides a concrete illustration of that dependence, strengthening the point just made.

• 3) The statement that "the machines are very stern masters" is a natural generalisation after describing people's servitude to machines.

• 4) The detailed description of how machines must be maintained (coal, petrol, oil, temperature) explains why they behave like stern masters, providing the necessary specifics.

• 5) The final sentence about machines growing sulky and refusing to work if not fed follows immediately after the maintenance details and gives the consequence, completing the logical chain.

Therefore the most logical order for the middle sentences between the fixed first and last sentences is: Machines were made to be man's servants... → Already most men spend most of their lives looking after and waiting upon machines. → The machines are very stern masters. → They must be fed with coal, and given petrol..., keeping the opening and closing sentences fixed.