Choose the correct pronoun for the sentence: "Either my sister or my brother will give (his or her, their) presentation tomorrow?"

In the sentence, "Either my sister or my brother will give (his or her, their) presentation tomorrow," the correct choice is "his or her."

The use of "his or her" is appropriate when referring to a singular subject that could be either male or female, which is the case here as "either my sister or my brother" refers to one of the two individuals. This expression maintains gender neutrality and grammatically agrees with the singular subject of the sentence.

While "their" has become increasingly common in modern usage as a singular, gender-neutral pronoun, traditional grammar rules dictate that a form like "his or her" is still more precise in contexts where the gender of the subject is specified as being either male or female. Therefore, "his or her" is the most formally correct option to use in this situation, upholding the specificity and clarity of the pronoun choice.