‘P’ will be the first part of the given sequence as the expression ‘perhaps a house was on fire’ is used in the context of ‘sound of fire engines’ in S1. ‘S’ will follow next as it states his reaction when he thought that his house was on fire, that is, he ‘rushed out to see’. ‘R’ will come next as it tells about the happening that was taking place outside. ‘Q’ will come next as the pronoun ‘they’ refers to ‘policeman’ in ‘R’. Hence, PSRQ is the correct sequence. Thus, option (d) is correct