Aclause from sentence (i) has been turned into a(n) in sentence (ii).

(i) since she knew what the lecture was about, she didn't attend the meeting.
(ii) knowing what the lecture was about, she didn't attend the meeting.

a. infinitive
b. relative pronoun
c. compound predicate
d. phrase

D. Phrase

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.