The commercial which says four out of five dentists surveyed would recommend this particular brand of toothpaste to their patients represents an appeal to authority.
What is an appeal to authority?
When a writer or a speaker uses the appeal to authority, they claim that something is true as it was believed by the person who is said to be the authority for a subject.
When we talk about a toothpaste, dentists are the authority because they know oral care better. The brand that claims that it was recommended by 4 out of 5 dentists actually uses dentists as authority and is doing appeal to authority in its commercial.
Therefore the correct option is a.
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