Correct answer: A). Installing anti virus software
The antivirus is a software or a set of program that is made to prevent, search and detect and remove the computer virus and any other malware like trojans, worms etc.
This software is very important for the computer user to install and up-to-date because if it is not there then there are chances of getting a virus into the computer that may corrupt all the information in the system.
Hence, the correct answer would be option A.