‘R’ will be the first part of the given sequence as it contains thesubject and verb, that is, ‘We know that he sat for the examination’. ‘Q’ will follow next as it presents a condition with the word, ‘but’. ‘S’ will come next as it contains a verb, that is,’ we have not heard. ‘P’ will follow logically as it presents the other condition. Hence, RQSP is the correct sequence. Thus, option (b)is correct.