1569. What character can be added to both of these characters to give other characters? 其_ -> _包

Answer:

其  shi, so - that

包  HOU, tsutsu(mu) - wrap

Add 月:其+月 月+包 

月  GETSU, GATSU, tsuki - moon, month

期  KI, GO - time, period, term

胞  HOU - sac, sheath, placenta