Which of the following is true about layouts?

A layout is indeed a predefined structure for messages, making it a foundational component in creating consistent and engaging email or campaign designs. Layouts serve as templates that provide a format for placing various content blocks, including text, images, buttons, and more. This structure helps maintain brand consistency while allowing marketers to efficiently design emails without starting from scratch every time.

Layouts being a group of content blocks is also accurately stated; they organize and manage these blocks to facilitate an orderly design. However, layouts can and often do combine with other content blocks, further enhancing the design and flexibility of the overall message.

Given that the choices provided include both the correct statement about layouts being a predefined structure and the idea that they consist of a group of content blocks, the correct answer incorporates both points, distinguishing it from the other options that lack a full representation of the characteristics of layouts.