黄油在冰箱里放了一夜后变硬了。

The butter ___hardened after being left in the fridge overnight.

多年的战地记者经历让他对生死变得麻木。

Years of being a war correspondent made him ___hardened to life and death.

经过多年的争论，她对这件事的态度已经变得十分强硬了。

After years of debate, her ___hardened attitude towards this matter won't change.