Which excerpt from "ain't i a woman? " best refutes the anti-suffragist idea that women were too fragile to handle the right to vote?

The excerpt that best does that is the following one - I have ploughed and planted, and gathered into barns, and no man could head me!
This part of the speech clearly shows that this woman did a better job plowing and planting than any man ever could, and that she proved them wrong by beating them at their own game. She wants to show everyone that women are also strong and quite capable of anything, and especially voting and fighting for their rights.