工匠将金属缓慢加热然后冷却以消除内部应力。

The craftsman slowly ___annealed the metal to relieve internal stresses.

多年的失败经历磨练了他的意志力。

Years of failures ___annealed his willpower.

在实验中，我们通过加热和冷却使DNA片段退火。

In the experiment, we ___annealed the DNA fragments by heating and cooling them.