Answer:
They are required on all time lines. They are found on some time lines. They represent the events on time lines.
Protons electrons neutrons
They were discriminated against by potential employers.
Sumer is the earliest known civilization in the southern-Eastern Mesopotamia region.
During the bronze age, the area was known for the developed of anciest villages, cities and 'city-states'
These cities were called 'city-states' because they were similar to independent countries rather than a collective power.
Each city had their own kings, their own army, economy and laws. They traded with one another and often fought wars but were not a single political entitiy.
That is why they are called city-states.