Which sentence uses an objective case pronoun incorrectly?

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

4 answers

Would you say?

wrote back to I
or
wrote back to me
I sent him an attachment that included photos of the picnic.
I e-mailed him yesterday. This is the correct answer.
bv v