Directions: Each of the following items in this section consists of a sentence, parts of which have been jumbled. These parts have been labelled as P, Q, R and S. Given below each sentence are four sequences, namely (a), (b), (c) and (d). You are required to re-arrange the jumbled parts of the sentence and mark your response accordingly.

(P) and has led to numerous medical and scientific advances / (Q) in the mid 20th century / (R) the discovery of DNA / (S) has revolutionized the field of genetics