The correct answer is: A. RSPQ
The first sentence, S1, introduces the topic of the passage: the relationship between humans and machines. The second sentence, P, provides an example of how humans are dependent on machines: they must be given fuel and other resources in order to function. The third sentence, Q, further develops this idea by stating that humans spend most of their time looking after and waiting upon machines. The fourth sentence, R, provides a contrast to the previous sentences by stating that machines were originally created to serve humans. The fifth sentence, S, provides another example of how machines have become more powerful than humans: they will refuse to work if they do not get their meals when they expect them. The sixth sentence, S6, summarizes the main point of the passage: humans are becoming increasingly dependent on machines, and this may eventually lead to machines becoming the masters.
The other options are incorrect because they do not follow the logical order of the sentences. Option B, RSQP, puts the second sentence first, which does not make sense because it is an example that supports the point made in the first sentence. Option C, SPQR, puts the third sentence first, which does not make sense because it is a detail that supports the point made in the second sentence. Option D, SRQP, puts the fourth sentence first, which does not make sense because it is a contrast to the point made in the first sentence.