Please choose the correct answer to the question: The elements sulfur (S) and oxygen (O2) combine to form a substance called sulfur dioxide (SO2). Sulfur dioxide is also formed when coal and oil are burned. Sulfur dioxide can best be described as

Answer1: a metal Answer2: an atom Answer3: a compound Answer4: a nonreactive gas

Answer format: answer1/answer2/answer3/answer4
Answer: answer3