Which of these modes is a composite server mode?

Answer: Option C

COMPOSITE: This option is incorrect. "COMPOSITE" is not a recognized server mode in MySQL.
COMPOSITE_MODE: This option is incorrect. "COMPOSITE_MODE" is not a recognized server mode in MySQL.
COMPOSITE_SERVER: This is the correct option. "COMPOSITE_SERVER" refers to a composite server mode in MySQL. In this mode, the server supports a combination of features from different server modes, allowing for flexibility in configuration and behavior. It is a composite mode as it combines characteristics of other server modes.
ANSI: This option is incorrect. "ANSI" typically refers to a SQL standard, but it is not a server mode in MySQL.

Therefore, the composite server mode among the options provided is Option C: COMPOSITE_SERVER.