After spending two hours trying to solve an engineering problem, Amira finally gave up. As she was trying to fall asleep that night, a solution to the problem popped into her head. Amira's experience best illustrates .

Ongoing civil wars western roman empire finally collapsed476 c.e. romulus, the last of theroman  emperors in  the west, was overthrown by the germanic leader odoacer, who became the first barbarian to rule in rome. the order that the  roman empire  had brought towestern  europe for 1000 years was no more.

Clean air provides nitrogen