Mr. Rosencrantz says that he knows which class period has the 1943 penny. He reveals the following pieces of information:​ Pennies made since 1982 have a density of 7.2 grams/milliliter.​ Almost all pennies made before 1982 have a density of 8.8 grams/milliliter.​ The exception is pennies made in 1943, which have a density of 7.9 grams/milliliter.​ In which class period is the student who has the penny from 1943?