UPSC CDS English Ordering of Words in a Sentence Part 2 Questions

‘P’ will be the first part of the given sequence as per the subject-verb agreement rule, that is,“animals are”. ‘Q’ will come next as ‘passing of the seasons’ is used in terms of ‘able to measure’, that is, it is talking about the ability of animals to measure the passing of the seasons. SR will make a pair together as it states the reason how they are able to measure, that is, by recognising the changes in day-length. Hence, PQSR is the correct sequence. Thus, option (a) is correct.