Which of These Observations Is Probably Due to a Difference

Multiple Choice

Which of these observations is probably due to a difference in cohorts?​

A) Most of today's 20-year-olds have quicker reaction times than their grandparents.
B) ​Most of today's 20-year-olds have less money saved or invested than their grandparents.
C) ​Most of today's 20-year-olds know less than their grandparents about the Vietnam War.
D) ​Most of today's 20-year-olds attend dances and movies more than their grandparents.