Which, "up" from the options below is functioning as an adverb?

-Up is an adverb, a preposition, and an adjective.
-Up is the opposite of down. It refers to the movement to a higher level.

অপশনে প্রদত্ত চারটি বাক্যের মধ্যে,
- Their service should be up by noon. (এখানে Up ব্যবহৃত হচ্ছে Adjective হিসেবে। )
- Their music is always upbeat. (Upbeat শব্দটি adjective, যার অর্থ: সুখকর, আনন্দময়)
- They had their ups and downs of luck. (Ups and downs is an idiom, যার অর্থ: a succession of both good and bad experiences.)
- They live up the mountain. (এখানে Up শব্দটি ‍adverb. কেননা এটি verb সংঘটিত হওয়ার location বোঝাচ্ছে)

Source: Cambridge Dictionary, Grammar reference.