1230. What character can be added to both of these characters to give other characters? 馬_ -> _母

Answer:

馬  BA, uma, ma  - horse

母  BO, haha - mother

Add 主:馬+主 主+母 

主  SHU, nushi, omo - lord, main

駐  CHUU - stop, reside

毒  DOKU - poison