778. What character can be added to both of these characters to give other characters? 矢_ -> _及

Answer:

矢  SHI, ya - arrow

及  KYUU, oyo(bu), oyo(bosu) - reach, amount to, match, equal

Add 口:矢+口 口+及 

口  KOU, kuchi - mouth

知  CHI, shi(ru) - know

吸  KYUU, su(u) - suck, inhale, smoke