How can non$-$skippable in$-$stream ads impact viewer experience and what is their cost structure?

$2$ points

A$)$ They are always free and unobtrusive

B$)$ They can be perceived as intrusive but ensure full message delivery, and are charged on a Cost$-$Per$-$Mille $($CPM$)$ basis, making it crucial to target the right audience with high$-$quality ads

C$)$ They are only shown to subscribers

D$)$ They are billed per click