‘P' will be the first part of the given sequence as it is in continuation with the previous statement and points out its cornerstone. 'S' will follow next as it begins with the words, 'this symbol' and refers back to 'P'. 'Q' will follow next as it is in contrast to the previous statement and talks about the changes. 'R' will come at the end as it begins with the word, 'moreover' and adds to the information provided in previous statements. Hence, PSQR is the correct sequence. Thus, option (b) is correct.