"His or her" would technically be the best fit, since it is acknowledging both genders, but it is very common to use "their" any most people wouldn't consider it wrong. <span />
Answer:
Explanation: Nominative and Objective
For example, in the sentence, "The dog ran," "dog" is the nominative because it's the performer of the verb "ran." An objective refers to a recipient or object of a verb or preposition
