Which of these is an XSS (Cross-site scripting) injection attack?

A. An attack that inserts malicious code into a website and targets the users of a service.
B. An attack that targets a whole website and uses database commands to delete or steal data and run other malicious commands.
C. An attack where attackers fool an employee into letting them into a restricted area or building.
D. An attack that overloads a system with ICMP echo requests to overwhelm it, preventing legitimate users from accessing it.