巨石滚下山坡时碎裂了。

The boulder ___crumbled as it rolled down the hillside.

受伤的士兵拖着沉重的步伐穿过泥泞的道路。

The wounded soldier ___stumbled through the muddy road with heavy steps.

那个大个子一拳重重地打在了小偷的脸上。

The big guy ___clobbered the thief right in the face with his fist.