UPSC 2017 CDS I English Paper

‘R’ will be the first part of the given sequence as ‘Researchers in the 1940s makes a logical phrase together. ‘P’ will follow next as it tells the discovery done by the researchers, that is, the research about the “allergic reactions”. ‘S’ will come next as it states the reason of ‘allergic reactions’, that is, they are brought about by the liberation of ‘histamine’. ‘Q’ will be the last part of the given sequence as it states the place of liberation, that is, in the bloodstream. Hence, RPSQ is the correct sequence. Thus, option (a) is correct.