Vaccination to prevent diseases. Vegan diets or whatever diets will not prevent them from having a better immune system to fight off such diseases
Yes, it is because they were there and didn't take it from someone else.
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Credibility of the source is checking the degree of authenticity of a source
(You want to know how reliable is this information?)
There are multiple factors that can help to check its credibility:
Is the author of the source trusted?
Is the background of the source safe?
Is it a primary or secondary source?
Have the source become unaccurate or
obsolete due to time?
Is there any motive or signs that the source is biased?
