PLZZZ HELP IM NOT GOOD WITH MY ENGLISH CLASS WILL GIVE RAINLIEST IF CORRECT!!! THE STUFF IN PARATHESIES IS THE UNDERLINED STUFF IN THE QUESTION

Classify the underlined part of the following sentence by the type of phrase or clause it is.

Obsidian, (which was used by early man to make arrowheads), is a naturally occurring glass.
A.
essential adverb clause
B.
nonessential adjective clause
C.
nonessential adverb phrase
D.
essential adjective phrase