If advertising succeeds in enhancing brand loyalty among consumers, it tends to enhance the monopoly power of the seller.

This statement is TRUE.

Explanation:

To enhace the monopoly power of a seller, means that one seller can monopolize or have more power over the market of certain products. What advertising does when succeeding is promoting one brand, generating consumers to buy only that same brand.

The consumer´s loyalty generates the monopoly of the market, making consumers only choose this same brand. This is why advertising is so powerfull and afects directly on the economy.

d. i assume the underlined word is "role." reformat if it isn't.

explanation:

role is closest to part because when replacing words, "playing a vital decision," "playing a vital activity," and "playing a vital dollar" don't make logical sense. the only meaningful choice is "playing a vital part."

this fits one of merriam-webster's definitions of role: "a function or part performed especially in a particular operation or process."