In the paragraph you provided, the word that means the same as "authentic" is "genuine."
All around the world millions of people watch hundreds of new movies each year. Most people are aware that these movies have actors and actresses, directors, stunt, doubles, and camera operators, but have you ever wondered how the crack of the bat and a baseball scene sounds so authentic, even though the camera must be dozens of feet away, which word means the same as authentic, as it is used in the paragraph.
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