Answer:
"at"
explanation:
Preposition- shows a relationship between a noun and pronoun in a sentence
noun- a person place or thing.
verb- an action word
adjective- a word that modifies a noun or noun phrase or describes it's referent.
pronoun- part of a speech that can be used to replace a noun
definite article- expresses an English word "the", indicates a specific person or thing
adverb- a word that describes a verb or an adjective
"Shrek" is a noun
"heard" is a verb
"the" is an adverb or definite article
"carolers" is a noun or verb
"singing" is a noun or verb
"at" is a preposition
"his" is a pronoun, noun, or an adjective
"neighbor's" is a noun, adjective, or verb
"front" is a noun, adjective, or verb
"door" is a noun