She worked as . . . . . . . . waitress.

The correct answer is D. no article.

The word "waitress" is a common noun, which means it refers to a general class of people. Common nouns are not preceded by articles unless they are specific or unique. In this case, the waitress is not specific or unique, so no article is needed.

Here are some examples of when an article would be needed:

• She worked as a waitress at the local diner. (The diner is specific, so the article "a" is needed.)
• She worked as the waitress for the president. (The waitress is unique, so the article "the" is needed.)

I hope this helps!