Choose the question that correctly asks who performed the action of inviting the strange guest.

A guy in a full dinosaur suit just walked into your living room. Since you definitely didn't invite him to the party, you turn to your roommate and ask: "___"

The correct answer is Who invited the dinosaur?.

You need a subject question because you want to know the identity of the person who performed the action (the subject). Therefore, you drop the auxiliary verb did and put the main verb in the past tense: "Who invited the dinosaur?"

"Who did the dinosaur invite?" is a perfectly formed object question, but it asks the wrong thing! It asks which lucky person received an invitation from the dinosaur.