Considering the available options, according to a common idiom, if you have proven the strength of your character, you have shown your "mettle."
Mettle is a vocabulary word used to describe the individual's ability to withstand the difficulties of a situation or condition.
In other words, mettle can be defined to mean endurance and resilience.
Hence, in this case, it is concluded that the correct answer is option D. "Mettle."
Learn more about Idioms here: https://brainly.com/question/4637832
