It's the same reasoning as why insurance gives better deals to people of greater age.. They are seen to have more experience and be more "mature " to drive safer if you have more years driving your insurance goes down.. same concept
An extrovert is someone who is outgoing and socially confident
It helps by keeping the food in a better position in the body and separates good from bad
The correct answer is C.
An author's credentials can determine a health source's credibility. None of the other options would apply to credibility. When it comes to health, if you want to make sure that what you are researching or reading is authentic and reliable you need to find out whether the author is a professional health expert or not. You can do this by finding out their credentials.