‘Q’ will be the first part of the given sequence as the relative pronoun ‘who’ is used in order to give further information about ‘my married aunt’. P will come next in order to maintain the rule of subject-verb agreement. S will follow next as it continues the fact of ‘lot of problems’ as mentioned in P in the form of ‘misunderstandings’ in this part. ‘R’ will be the last part of the given order as it is stating the reason of problems and misunderstandings. Hence, QPSR is the right sequence. Thus, option (b) is correct.