Regulations under the federal trade commission's advertising substantiation program established that supposed experts used in advertisements must be qualified experts in their field, and celebrities must the products they endorse.

use      

Explanation:

The answer is -- "use".

               The Federal Trade Commission was established as a independent agency in the US government. It was established at the year 1914.

               The main purpose of the Federal Trade Commission was to prevent illegal methods and unfair means of competition in business and commerce that they use to advertise their product.

              Under the regulation of Advertising Substantiation Program as laid down by the Federal Trade Commission of the US, the experts those who are used in the advertisement must be a qualified and experts in that respective field and the celebrities whose stardom is used to influence people by showing them in the advertisement must also use the mention product that they endorse.

Thus the answer is -- "use".

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