2551. What character can be added to both of these characters to give other characters? 日_ -> _台

日  NICHI, JITSU, hi, ka - sun, day

台  DAI, TAI - stand, pedestal, platform

Add 月:日+月 月+台  

月  GETSU, GATSU, tsuki - moon, month

明  MEI, MYOU, aka(rui), a(keru) - bright

胎  TAI - womb, uterus