Final answer:
The only acceptable piece of jewelry that a food worker can wear under a glove is a plain band ring, since other types of jewelry can harbor bacteria or present physical hazards in food preparation.
Step-by-step explanation:
The acceptable piece of jewelry that a food worker can wear under a glove when preparing food is a plain band ring. Items like bracelets, watches, and necklaces are not permitted because they can accumulate dirt and bacteria, posing a risk for food contamination. Furthermore, wearables such as watches and bracelets can also potentially fall into food, creating a physical hazard. Therefore, the correct answer to the question is (c) Ring.