二者必居其一
èr​zhě​bì​jū​qí​yī

either one or the other

  1. 二者 èr​zhě pronoun
    both
    the two of them; both parties; can also mean "neither" when used with a negative word
  2. 必 bì adverb
    certainly
    certainly; surely; inevitably; necessarily
  3. 居 jū verb
    to occupy
    to occupy a certain position; to be situated in; to hold a post
  4. 其一 qí​yī
    the first; one of them
    The first of several points or options; firstly; one of the items mentioned