This is how I would combine it:
"I think Robert, Mary, Jane, Andrea Lee, and Ann Milton should be on the planning committee."
I used FOUR commas, so THE CORRECT ANSWER IS B.
In the sentence, four commas need to be added to properly separate the names, resulting in the sentence: "I think Robert, Mary Jane, Andrea Lee, Ann, and Milton should be on the planning committee." The correct answer is B: Four.
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