Considering the idiomatic expression, according to a common idiom, if you have proven the strength of your character, you have shown your "mettle."
This is because mettle is a vocabulary word that means an individual's ability to cope well with difficulties; spirit and resilience.
Mettle is sometimes referred to as courage or the heart or bravery to carry on during the turbulent period.
Hence, in this case, it is concluded that the correct answer is "Mettle."
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