Which statement is true concerning a functional iRule.

iRules are based on the Tcl (Tool Command Language) scripting language, which is an open-source language, not proprietary.

Every iRule must contain at least one event declaration (e.g., `when CLIENT_ACCEPTED`, `when HTTP_REQUEST`). These events define the specific points in the traffic flow lifecycle where the iRule's commands and logic are triggered and executed. Without an event, the iRule would never be invoked by the BIG-IP system.

An iRule does not necessarily require a conditional statement; it could perform actions unconditionally upon an event trigger, such as logging every connection.

An iRule can perform many functions, such as logging or header manipulation, without ever explicitly assigning a pool, as the virtual server itself might have a default pool or the iRule's purpose is not pool selection.