‘Q’ will be the first part of the given sequence as it refers back tothe previous statement which is clearly indicated form the word,‘therefore’. ‘P’ will follow next as it is in contrast to the previousstatement which is indicated from the word, ‘but’. ‘S’ will come next as it is in continuation with the previous statement and gives anexample of the thing talked about ‘R’ will follow logically as it further adds to the ‘disadvantages’ mentioned the previous statement which is clear from the word, ‘moreover’. Hence, QPSR is the correct sequence. Thus, option (b) is correct.