A. A cybersecurity attack
B. A social engineering tactic
C. A security mechanism that requires users to provide two forms of identification to access an account or system
D. A programming language

Solution

C. A security mechanism that requires users to provide two forms of identification to access an account or system

Explanation

Two-factor authentication (2FA) is a security mechanism that requires users to provide two forms of identification, typically something they know (e.g., a password) and something they have (e.g., a smartphone or token), to access an account or system.