Complete the snooty food critic's latest scathing review by selecting the correct formal phrase.

The alarming enthusiasm _____ the waiter presented the deep-fried grasshoppers completely ruined my appetite.

The correct answer is with which.

We do things "with enthusiasm," so the relative clause needs the preposition "with." In a formal register, the preposition is moved to the front of the relative clause, right before which. Remember, the relative pronoun "that" can never immediately follow a preposition!