Which sentence uses an objective case pronoun as an indirect object?
I sent him an attachment that included photos of the picnic.
The indirect object him identifies to whom the action of the verb <u>sent</u> is performed.
<em>Wrong options:</em>
I e-mailed him yesterday.
(The direct object <em>him</em> is the receiver of action within this sentence: I emailed him).
He wrote back to Bob and I with an answer to our questions.
(I is not an objective case pronoun; it should be "He wrote back to Bob and <u>me</u>...")
So, once again, the answer is the 2nd sentence (I sent him an attachment that included photos of the picnic.)