Which is the adverb phrase in the sentence?

During a roundup, she watched cowboys on horseback at work and learned their techniques.

a. During a roundup

b. at work

c. on horseback

b. at work

Example:

In the given statement, "The Caribbean sea is a great location for deep-sea fishing." The phrase "a great location for deep-sea fishing" is the adjective phrase of the sentence.

Phrases are group of words that doesn't have a complete thought unlike clauses that can stand alone since it has a subject and predicate whereas a phrase doesn't.

An adjective phrase is one type of phrase to describe a noun or pronoun subject in a sentence. Also is adverb clause.