Help the hungry detective finish his secret case notes by choosing the correct article for each blank.

I disguised myself as an undercover cop and sat in the diner. I ordered a sandwich with extra pickles, and then I kept my eyes entirely focused on the manager of the restaurant.

I disguised myself as an undercover cop...

We use "an" when stating someone's profession or role if the word begins with a vowel sound (like the "u" in undercover).

I ordered a sandwich with extra pickles...

We use "a" to introduce a new, non-specific singular item that starts with a consonant sound.

...and then I kept my eyes entirely focused on the manager of the restaurant.

We use "the" because the phrase "of the restaurant" makes it a specific, known person. We aren't talking about just any manager; we mean that exact one!