This article is from the Puzzles FAQ, by Chris Cole chris@questrel.questrel.com and Matthew Daly mwdaly@pobox.com with numerous contributions by others.
H, H, L, B, B, C, N, O, F ?
series/series.02.s
Answer 1: N, N, M, A The first letters of the symbols for the elements.
Answer 2: N, S, M, A The first letters of the names of the elements.
 
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