harden|hardened|hardening

混凝土需要几天时间才能完全硬化。

The concrete takes several days to fully ___harden.

多年的艰苦生活使他的心变得坚硬冷漠。

Years of hardship have ___hardened his heart.

这种粗麻布袋子是用硬化材料做的，非常结实耐用。

These coarse sacks are made of ___hardening, which is strong and durable.