Final answer:
The option that is not a data transmission control is C) File labels. Data encryption, echo checks, and parity checks are all valid controls for transmitting data securely and accurately.
Step-by-step explanation:
The data transmission control that is not among the options provided is C) File labels. Data transmission controls are techniques or measures used to ensure the integrity and security of data as it is transmitted from one location to another. Echo checks, B) Data encryption, and D) Parity checks are all legitimate data transmission controls.
Echo checks involve sending data to a remote system, which then sends the same data back to the source to verify its accuracy. Data encryption is the process of converting data into a coded format to prevent unauthorized access. Parity checks involve adding an additional bit to data to check for errors during data transmission. In contrast, file labels are typically used for data storage and organization rather than for controlling data transmission.