as cheerful as a lark字面意思像云雀一样快活，引申为欢呼雀跃；兴高采烈；非常快乐。

【例句】
The old man became as cheerful as a lark when he heard that his grandchildren were coming for a visit.
老爷爷听说他的孙子孙女们要来他家里玩，简直高兴极了。

She lived in the village with her grandparents as cheerful as a lark.
她同祖父母一起住在乡间非常快活。