This is a screen shot of my [DataDriven] Excel chart I learned how to create in Lab.

The question is:
I wonder whom he bribed to get the contract?
(1) Sentence is grammatically correct
(2) Sentence is not grammatically correct
(3) I don't know

The correct answer is (2) because every verb with a tense (-ed/-ing) must have a subject, and if it's a nominative case, then who is used.

My class got this answer correction, but there was some discrepancy. I feel as if I should review the lesson just to make sure all of my students grasp the concept of who/whom.