improver
  改進者;改進物;學徒,練習生
  Im·prov·er n. One who, or that which, improves.
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  improver
       n 1: someone devoted to the promotion of human welfare and to
            social reforms [syn: humanitarian, do-gooder]
       2: a component that is added to something to improve it; "the
          addition of a bathroom was a major improvement"; "the
          addition of cinammon improved the flavor" [syn: addition,
           add-on]