Question $21$ this advertising probably caused

a$.$ Adrian's demand to become less elastic, and the cookie snack industry is likely a monopoly industry.

b$.$ Adrian's demand to become more elastic, and the cookie snack industry is likely a monopolistically competitive industry.

c$.$ the cookie snack industry to become a monopoly, when prior to advertising, it was probably perfectly competitive.

d$.$ the cookie snack industry demand to become less elastic, and Adrian's demand was unaffected.

e$.$ Adrian's demand to become less elastic, and the cookie snack industry is likely a monopolistically competitive industry.