Identify the italicized word according to its class in structural linguistics.

I do (not) know what to say.
conjunction
preposition
auxiliary
interrogative
empty word

What's your choice?

i chose empty word but im not sure if it is right

No it is wrong.

im not sure what it is?

you are the real mvp, slashing the trash, so now I know it's not empty word.

you have to have a horse wang

preposition