6. How do scientists determine when an era begins and when it ends?

the part i "agree with' is " it should not matter what color their skin is or what their cultural beliefs are." but for the main part i agree with it all or if cause now and days there are some people don't get the job cause there skin color and there beliefs and some times they don't even get the same repest as white people. we are all equal.

your answer is a. hope this : )