这些骷髅展示了死亡的主题。

These ___skulls illustrate the theme of death.

医生仔细检查了患者的头骨X光片。

The doctor carefully examined the X-ray of the patient's ___skull.

这个数学题太难了，我的脑袋都要炸了。

This math problem is so hard it's making my ___skull hurt.