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支撑词；代替词

A term used in some grammatical descriptions to refer to a meaningless element introduced into a structure to ensure its grammaticality. Such words are also referred to as empty, because they lack any semantically independent meaning.

某些语法描写用“支撑词”来指一个引入某个结构以保证其合语法性的无意义成分。这类词有时也称作空成分，因为缺乏任何语义上独立的意义。