爬山是一项非常费力的活动，尤其是当坡度很陡的时候。

Climbing mountains is an ___effortful activity, especially when the slope is steep.

他费力地抬起沉重的箱子，每一步都很小心翼翼。

He made an ___effortful attempt to lift the heavy box, moving carefully with each step.