Read the paragraph from the introduction [paragraphis down below].

Lombardi works for various scientific groups, including the American Museum of Natural History, the Woods Hole Group, and the University of Rhode Island. One of his areas of expertise is deepwater
coral reefs. He often dives in a 400-foot-deep reef along Exuma Cays in the Bahamas. These are a group of islands
near Florida.

What is the meaning of the phrase "areas of expertise" in this paragraph?
a
islands he enjoys
b
places he visits often
c
groups he works with
d
subjects he knows well