Which ad format is known for its segmented design and is initially sized at 300×1050?

The correct choice is the Portrait ad, which is characterized by its tall and narrow layout, making it distinct from other ad formats. Its initial size of 300×1050 pixels allows it to be visually prominent in a vertical context, which is well-suited for mobile and desktop interfaces.

Portrait ads are often used to highlight specific messages or campaigns, taking advantage of their unique dimensions to draw users' attention more effectively than standard banner formats. The segmented design allows for creative uses, such as incorporating images or interactive elements that can engage viewers, making it a preferred option for advertisers wanting to stand out.

In contrast, formats like the Filmstrip, Billboard, and Push-down ads have different characteristics and dimensions that don't align with the specific height and width of a Portrait ad. Understanding the specific attributes of each format helps advertisers choose the best approach for their marketing objectives.