Question

which of these is an authentication factor?

who you know

what you have

case sensitivity

where you go

Explanation:

Authentication factors are used to verify a user's identity. The three main types are something you know (e.g., password), something you have (e.g., token, mobile device), and something you are (e.g., biometrics). "What you have" is a valid authentication factor. "Who you know" is not relevant to authentication. "Case sensitivity" is a property of passwords (something you know) but not a factor itself. "Where you go" is not an authentication factor.

Answer:

What you have