Block Kit layouts are represented as structured JSON objects and arrays when interacting directly with Slack APIs. Each block is represented as an object containing a `type` field together with properties appropriate to that block. Multiple blocks are normally placed inside a `blocks` array in the visual order in which Slack should render them. For example, a section block can contain a text composition object and an accessory such as a button. Slack's Block Kit documentation explicitly describes application interfaces as specially structured JSON. Language SDKs and Bolt frameworks may provide native-language objects, classes, or dictionaries that make construction more convenient, but those structures ultimately correspond to Slack's JSON payload representation. XML, YAML, and CSV are not the API representation used for Block Kit layouts. Therefore, C is correct.