A generational cohort $($e$.$g$.,$ Baby Boomers, Generation X$,$ Millennials, etc.$)$ is a group of people $\_\_\_\_\_.$

a$.$

who mature during roughly the same historical period, which is often only defined after they reach adulthood

b$.$

who are members of the same demographic group

c$.$

who share the same birth year

d$.$

with the same beliefs and values, and therefore the same attitudes

e$.$

who are the children of the previous generation