The following two-factor authentication (2FA) methods can be used to secure a GitHub account:
* A. Authenticator app: You can use an authenticator app (like Google Authenticator or Authy) to generate time-based one-time passwords (TOTP) for logging in.
* C. GitHub mobile: The GitHub mobile app can also be used to receive 2FA codes, adding convenience for users who prefer to manage everything from their mobile devices.
* D. Security keys: Physical security keys (such as YubiKeys) can be used as a strong form of 2FA, requiring physical access to the key to authenticate.
Security questions and Single sign-on (SSO) are not considered 2FA methods in the context of GitHub account security.