感谢O大多次指教。+ P; [/ F7 X- E3 t# r' p
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关于原因,看到了wikik上对于function words的一段说明5 ]! T7 X! {/ O n
Dictionaries define the specific meanings of content words, but can only describe the general usages of function words. By contrast, grammars describe the use of function words in detail, but treat lexical words in general terms only. % [8 g0 ?4 X: ]6 i- U(https://en.wikipedia.org/wiki/Function_word)