SI: Don’t you think that the housefly is a nuisance ? S6 : When you see a fly rubbing its legs together, it is just cleaning itself, and scraping off some of the material that has gathered there. P : For ages that’s what man considered the fly to be — just a nuisance. Q : It was discovered that these flies carried disease germs that cause the death of millions of people every year. R : But now we know that the innocent looking housefly is one of man’s worst enemies. S : It makes an irritating buzzing sound; it annoys you when it crawls on your skin; and so on. The proper sequence should be
- AR Q P S
- BP Q S R
- CQ P R S
- DS P R Q
Explanation
S expands S1's 'nuisance': the buzzing and crawling on skin. P echoes the old view -- 'for ages that's what man considered the fly to be'. R pivots with 'but now': the fly is one of man's worst enemies. Q supplies the evidence: disease germs killing millions yearly. S6 closes on the fly rubbing its legs and scraping off gathered material, tying back to the germs in Q. Hence SPRQ, i.e. option D.