Answer B is not correct because Cross-site Scripting (XSS) is not a brute force attack.
Answer C is not correct because the statement "Cross-site Scripting is when executives in a corporation are attacked" is not true. XSS is a client-side vulnerability that targets other application users.
Answer D is not correct because the statement "Cross-site Scripting is an attack where code is executed from the server side". In fact, XSS is a method that exploits website vulnerability by injecting scripts that will run at client's side.
Therefore only answer A is left. In XSS, an attacker will try to inject his malicious code (usually malicious links) into a database. When other users follow his links, their web browsers are redirected to websites where attackers can steal data from them. In a SQL Injection, an attacker will try to inject SQL code (via his browser) into forms, cookies, or HTTP headers that do not use data sanitizing or validation methods of GET/POST parameters.
Note: The main difference between a SQL and XSS injection attack is that SQL injection attacks are used to steal information from databases whereas XSS attacks are used to redirect users to websites where attackers can steal data from them.

Each rule also has an action, which determines whether you monitor, trust, block, or allow matching traffic.
Note: With action "trust", Firepower does not do any more inspection on the traffic. There will be no intrusion protection and also no file-policy on this traffic.

In this question, the engineer was trying to secure the connection so maybe he was trying to allow SSH to the device. But maybe something went wrong so the connection was failing (the connection used to be good). So maybe he was missing the "crypto key generate rsa" command.