reasoning - What part of speech is "before" in the phrase "before we meet again"?

Identify the part of speech of the word in bold:

It will be five years before we meet again.

4 options:

• Preposition


• Adverb


• Conjuction


• Adjective

Now, According to my knowledge, "before" is an adverb. However the correct answer was - conjunction. What am I missing?

Answer

Traditionally, it's referred to as a "subordinating conjunction" because it introduces a subordinate clause.

But in modern grammar, it's analyzed as a preposition that takes a clause rather than a noun phrase as a complement.