how can having 100 trillion microorganisms on and in the human body keep us healthy?

The correct answer is because the microorganisms that live in us help us in the most basic vital functions.

Explanation:

These microorganisms determine the immune system's ability to recognize "foreign" factors and distinguish them from harmless ones, maintain balance within the microbial communities themselves without attacking themselves. Also, they are the first barrier against harmful microbes that are outside, behaving like a living defense that is always changing.

Those found in the intestinal area are fundamental to the processing and absorption of nutrients, indispensable to extract the essential nutrients we need to function.

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explanation:

in scientific notation, the value of the  speed of light in a vacuum

  will be written as 2.995 * 10^8. when this value is represented in the form of

  a * 10^b, then, a = 2.995 and b = 8.

the value of the speed of light in a vacuum given above can also be rounded up to approximately 300000000. in this case, the scientific notation will be written as 3 *10^8.