'R' will be the first part of the given sequence as it refers to the previous statement, which is clear from the words, 'the chunk of the relief'. 'S' will follow next as it is in continuation with the previous statement and throws light on the further classification. 'Q' will come next as it refers back to the previous statements which is clear from the words, 'earlier these'. 'P' will come at the end as it sums up all the points in the previous statements, which is clear from the word, 'together'. Hence, RSQP is the correct sequence. Thus, option (a) is correct.