A marketer wants to create a mobile campaign for a new astronomy app. They also want their ads to serve on modern browsers.Which ad inventory option should they work with?

The marketer needs to reach users on mobile devices (smartphones) and ensure ads serve on modern browsers. Smartphone web inventory directly addresses both of these requirements, as it targets users browsing the internet on their smartphones. Desktop web inventory is also included because modern browsers are prevalent on desktop computers, ensuring broad reach for the "modern browsers" requirement. Mobile in-app inventory would reach smartphone users but doesn't specifically target "modern browsers" as apps use their own rendering engines. In-stream and out-stream video inventory are ad formats, not inventory types that directly fulfill the "modern browsers" requirement across devices. Tablet inventory is too restrictive, as it excludes smartphones and desktop users who use modern browsers.