5 lucky randomly selected correct answers will win a great popular science book, PLUS an extra prize for the funniest answer (which doesn't have to be correct!) Good luck!
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T&Cs Promoter is BBC Magazines Ltd; entrants 16yrs + and UK resident. Winners are 5 randomly selected correct answers from comments on BBC Focus website or sent to firstname.lastname@example.org before 16/12/10. One guess per entrant.