difficult / hard, probably impossible

examination, exam, test / quiz

国家: a nation / 国歌: a national anthem / 国花: a national flower / 刻下: the present / 酷夏: a terribly hot summer / 骨化: ossification

梱: wrapped package; bale / 狐狸: foxes and tanukis; sly trickster, stealthy evildoer

狐狼: foxes and wolves; cunning and malicious person

骨炭: boneblack

Contraction of ことだ (koto da).

Alternative form of こうる (kōru, “to pack”)

to grow stiff / to put skilled effort into

(colloquial) from here.