Answer:
Hey!- Interjection
behind- preposition
because- conjunction
birthday- noun
present-noun
Step-by-step explanation:
hey! : someone says it as an interjection, they interject
behind : preposition : shows relationship between objects (often place; like up, down, or in this case, behind)
because : it connects two parts of a sentence
birthday and present : they are things.
hope this helps!