The correct option is Default environment variables are predefined by GitHub and every step in the workflow can access them.

GitHub provides a standard set of variables for each job so every step can read them without extra configuration. These include items such as GITHUB_SHA and GITHUB_REF and they are available as normal shell environment variables. You can also read their values in expressions through contexts such as the github context, which confirms they are not limited to a special env context.

Default environment variables can be referenced only through the env context defined in the workflow file is incorrect because the defaults are real environment variables that steps can read directly, and they can also be accessed through contexts. The env context is useful for variables you define in the workflow but it is not the only way to read the defaults.

Default environment variables are created only when a step writes to GITHUB_ENV during the run is incorrect because the defaults exist before any step runs. Writing to GITHUB_ENV creates or updates custom variables for subsequent steps in the same job and does not create the defaults.

Default environment variables are visible only to steps that explicitly request them is incorrect because the defaults are automatically available to all steps in a job and do not require an opt in.

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