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It would have helped to answer this question, if there were some options to choose from. I am answering the question based on what i understood. I hope that it helps you. The teeth rip and grind food into small chunks. This is also the main function of the teeth and it does help in the digestion of the food we take.
Education that result in understanding and the spread knowledge physics
The sentences are invalid and unsound.
<h3><u>Explanation</u>:</h3>
The fire is defined as the vigorous oxidation of a substance. Now oxidation can occur in presence of any oxidising agent. Like magnesium in presence of nitrogen in high temperature with a dazzling brownish flame to produce magnesium nitride. So fire can be produced in absence of oxygen.
Oxygen is present everywhere in world. So production of a whole room without oxygen is very tough to produce and costly process. So its very unsound.
Some examples of when friction is helpful are: to help the movement of tires. When you walk, and also, when you erase. :)
