5 introduces the paragraph and hence, can be the topic sentence. 2 will come next as the word "but"suggests a slight change in the theme 2 changes the theme mentioned in 5 51 make a mandatory pair as the pronoun “it says" in 1 refers to the theory or study mentioned in 5 3 will come next as England is the researcher who has been mentioned in 2 and 1 4 will come next as Paul Rosenberg reviews the theory mentioned in the previous sentences