commutable
  (a.)可取代的
  Com·mut·a·ble a.  Capable of being commuted or interchanged.
     The predicate and subject are not commutable.   --Whately.
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  commutable
       adj 1: subject to alteration or change; "the death sentence was
              commutable to life imprisonment" [ant: incommutable]
       2: capable of being exchanged for another or for something else
          that is equivalent [syn: substitutable]