Can anyone explain why there are only three grades of pass for GCSE, that is, A, B and C but there are five grades of failure, that is D, E, F, G and U.
Could it be that it is now considered politically incorrect to suggest that a candidate has simply failed an exam?
Kay Bagon Radlett, Hertfordshire
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Correction: Bill Cockburn and colleagues are developing plants that produce antibodies at the University of Leicester, not at the University of Birmingham as stated in the article 'How tobacco can fight pollution' (Technology, 16 July). We apologise for any confusion this error may have caused.
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