1603. What character can be added to both of these characters to give other characters? 言_ -> _頁

Answer:

言  GEN, GON, i(u), koto - say, speech

頁  KETSU, peeji - page

Add 川:言+川 川+頁

川  The "Sanbongawa" radical - river

訓  KUN - Japanese reading, teaching

順  JUN - order, sequence