Answer: Key-logger
Explanation: Key-logger is the device that is used in the capturing the keystrokes of the user and then recording it .They can be in the form of software or hardware.The recording made by key logger consist the data typed through the keyboard like email, messages, passwords .
Other options are incorrect because keyboard is the hardware device used for inputting data in the system, key-scanner is the input reading device in the form of library and rootkit is malicious collection of software to disturb the function of the computer system.Thus the correct option is key-logger.