On GitHub, certain actions automatically subscribe you to conversations so that you receive notifications about further activity in that thread.

Opening a Pull Request or Issue:

Option C is correct because when you open a pull request or issue, you are automatically subscribed to the conversation and will receive notifications for any updates.

Commenting on a Thread:

Option D is correct because commenting on an issue or pull request automatically subscribes you to that thread, ensuring you are notified of further comments or changes.

Being Assigned to an Issue or Pull Request:

Option E is correct because when you are assigned to an issue or pull request, you are automatically subscribed to notifications related to it.

Incorrect Options:

Option A is incorrect because pushing a commit to the default branch does not automatically subscribe you to conversations.

Option B is incorrect because being added as a repo admin does not automatically subscribe you to specific conversations unless you engage with them.