‘R’ will be the first part of the given sequence as it combines with the phrase ‘last summer’ in order to form the subject clearly. Q will come next in order to maintain the rule of subject-verb agreement. SP will make a pair together as ‘with phone calls’ is used in relation to ‘pestering’ and P will be the last part as ‘with phone calls every day’ makes a logical phrase together. Hence, RQSP is the right sequence. Thus, option (c) is correct.