harden

混凝土需要几天时间才能完全硬化。

The concrete takes several days to fully ___harden.

把黄油放在冰箱里会变硬。

The butter will ___harden if you put it in the fridge.

学校决定加强对学生手机使用的管理规定。

The school decided to ___harden its rules on students' phone usage.