Which sentence uses an objective case pronoun as a direct object?

I e-mailed him yesterday.
I sent him an attachment that included photos of the picnic.
He wrote back to Bob and me with an answer to our questions.

I'll be glad to check your answer.

I e-mailed him yesterday.

The sentence that uses an objective case pronoun as a direct object is: "I e-mailed him yesterday."

To identify the direct object in a sentence, you need to ask the question "Whom?" or "What?" after the verb. In this case, the verb is "e-mailed," and asking "Whom did I e-mail?" gives us the answer "him." The pronoun "him" serves as the direct object because it is receiving the action of the verb.

Therefore, "I e-mailed him yesterday" uses an objective case pronoun ("him") as a direct object.