Question: Signs in many stores and restaurants warn that microwaves are in use. What is the main reason for this warning?

  Options: 
 A. Some people do not like food cooked in microwave ovens.
 B. Microwaves sometimes affect people's sense of sight.
 C. Microwaves sometimes cause hair or teeth to fall out.
 D. Some people have pacemakers that may be affected by microwaves.
Answer: D