‘R’ will be the first part of the given sequence as it states the ‘other organs’ mentioned in the opening part, that is, ‘lungs or the liver’. ‘S’ will come next as per the subject-verb agreement rule. It will then be followed by ‘P’ as the contrasting word ‘but’ is showing a condition. ‘Q’ will be the last part of the given sequence as ‘that’ in ‘P’ is used in relation to ‘heart transplant’ in this part. Hence, RSPQ is the correct sequence. Thus, option (b) is correct.