According to the fifteenth amendment, which of these factors cannot be used to deny u. s. citizens the right to vote?

It seems that you have missed the necessary options to answer this question, but anyway, here is the answer. According to the fifteenth amendment, the factors that cannot be used to deny U.S citizens the right to vote are their income and gender. You can be denied by your age since there is a required age requirement in voting. Your race can be also be a factor to be denied since it is only for U.S citizens. 

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