Determine which punctuation rule is illustrated by the following sentence.

At our company retreat, I met employees from Tempe, Arizona; Denver, Colorado; and Honolulu, Hawaii.

a. Use a colon to join closely related independent clauses.
b. Use a semicolon to separate items in a series when one or more of the items contain internal commas.
c. Use a colon to separate items in a series when one or more of the items contain internal commas.