What part of speech is complex in this sentence a geometry problem stumped the parent?

In the sentence "A geometry problem stumped the parent," the word "complex" is not present.

Let's analyze the sentence:

* A - Article

* geometry - Noun

* problem - Noun

* stumped - Verb (past tense)

* the - Article

* parent - Noun

Therefore, the word "complex" is not a part of this sentence.