Final answer:
The correct punctuation in the given examples is option A, which uses a colon to introduce the list of companies. A semicolon separates independent clauses or complex list items, while a comma provides additional information or separates items in a simple list.
Step-by-step explanation:
The correct punctuation for the given sentence is the use of a colon because it is introducing a list of specific companies that the business conducts dealings with. The correct option is A. We conduct business with several East Coast companies: WorcesterTech, SouthBean, and HopkintonTeach. A colon is correctly used here to introduce a list. In contrast, a semicolon is more often used to connect independent clauses without a conjunction or to separate items in a list where the items themselves contain commas.
For an illustrative example, consider the sentence: The roof of that car was covered in Astroturf; a strange sight! Here, the semicolon is appropriate because it links two related but independent clauses. Now, consider the sentence: Quentin's father gave him a golden pocket watch, which was a priceless family heirloom. Here, a comma is used because the second clause is not independent and is instead providing additional information about the first clause.