Final answer:
To create a preset for a theme, the file to edit is config/settings_data.json. This file contains the theme's default settings and presets, which are applied upon the theme's initial load.
Step-by-step explanation:
You're asking about creating a preset for your theme, which is a common task when customizing themes on a platform such as Shopify. To create or edit a preset for your theme, the correct file to work on is indeed C) config/settings_data.json. This file contains the preset configurations that define the default settings when the theme is initially loaded. It's where you set the values that the theme will use if the user hasn't customized it further through the theme editor.
It's important to note that the settings_schema.json file defines the structure of the settings and often includes information about options available within the theme editor, while the theme.liquid file is the main layout file that includes the overall HTML structure of your theme.
The sections/preset.liquid doesn't typically exist; theme sections are individual .liquid files inside the sections directory and are used to create configurable blocks of content.