2437. What character can be added to both of these characters to give other characters? 北_ -> _台

北  HOKU, kita - north

台  DAI, TAI - stand, pedestal, platform

Add 月:北+月 月+台   

月  GETSU, GATSU, tsuki - moon, month

背  HAI, se, somu(ku), somu(keru) - back, height, act contrary to, avert

胎  TAI - womb, uterus