Select whichever preposition or determiner you consider the most appropriate for the blank space.
She is capable ___________ winning the race.

Correct option is C

The word that can be filled in the blank is ‘of’ to make the sentence grammatically and contextually correct.
• ‘Of’ is used to indicate relationship or possession, being a part of something, or belonging to.
• As per the context, the word ‘of’ fits very well & hence, it is the correct option.
Meanings of other given words:
• On - used to indicate position above and supported by or in contact with.
• At - used to indicate a specific time.
• Until - used to indicate the time something continues to happen.
• Thus, all the other given words have different meanings and do not fit in the context of the sentence.