In the Twelfth Night, what final proof does Sebastian need to ensure that Cesario is really Viola?

Question

her reference to her brother's watery death
her reference to her own age at the time of her father's death
her reference to her father, Sebastian
her reference to her father's mole

Answer 1

The final proof that Sebastian needs to ensure that Cesario is really Viola is her reference to her brother's watery death.