True they ruled from 403 bc till 404 bc
Sir John Harrington invented the flushable toilet in 1596, however the idea of a toilet has existed for thousands of years in much more primitive forms.
Causes of US failure in Vietnam include b) The United States supported corrupt leaders in Vietnam and d) Only a few US soldiers fought with honor.
One of the biggest issues of the Vietnamese war was that the United States went in because of anti-communism above all other reasons because of the Truman Doctrine. The South Vietnamese leaders were not well liked and were overall corrupt. The knowledge of this back home created a lot of public tension and actually caused soldiers to feel they weren't fighting for a good cause, or even commit war crimes as seen in the My Lai Massacre.
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Answer:
You did not provide the excerpt nor the answers so nobody can answer this.
Yes, it is true that linguists do not know for certain how language was developed by early humans, but they're able to determine that it started somewhere in Africa, due to human migration patterns.