Answer:
a) gross impressions
Explanation:
First of all, impressions are the times an individual member of an audience is exposed to a certain advertisement.
Gross impressions refer to the total amount of times a group of individuals (or households) that are exposed to a certain advertisement during a given media schedule or program.
A single individual might be exposed several times to the same advertisement, therefore the number of gross impressions may exceed the total audience of the media.
Gross rating points measure the audience of a media while gross impressions measure the number of times the audience is exposed to a certain advertisement.