QUESTION $49$

Keith uses Google Analytics to view his website analytics data. He is concemed about impressions, which

a$.$ determines how long it takes his webpages to load on users' devices

b$.$ are the number of times an ad is visible to users on a webpage

c$.$ is the average number of unique visitors his website receives on a daily basis

d$.$ gets users to spend long periods of time engaging and encourages them to return