A. is a period unified by a common theme, often social or political

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Explanation:

An era is a period unified by a common theme, often social or political. This can often be confused with a period, but it should be noted that an era is harder to define in terms of the various social elements of which it is comprised. 

so they can differentiate themselves from others as they saw themselves as the superior race. the star was basically a symbol that meant you are a less of a person than i am because of my race. the star was also degrading for those who had to wear it because they were aware of this and the nazis used the notion to make them feel less like a person.

probally   a few days after there called