1446. What character can be added to both of these characters to give other characters? 苗_ -> _古

Answer:

苗  BYOU, nae, nawa - seedling, sapling

古  KO, furu(i) - old

Add 木:苗+木 木+古 

木  MOKU, BOKU, ki - tree

菓  KA - cake, fruit

枯  KO, ka(reru), ka(rasu) - wither