Which of the following is a type of Electronic Attack?

The correct answer is jamming enemy communication systems, as it directly falls under the category of electronic attack. Electronic attack involves using electromagnetic energy to disrupt or deny an adversary's ability to communicate or effectively utilize their electronic systems. Jamming specifically targets enemy communication systems by emitting signals on the same frequency to overpower or interfere with their transmissions, thereby hindering their operational capabilities.

Other options, while relevant to electronic warfare, serve different purposes. Electronic emissions control refers to measures taken to minimize the unintentional transmission of electromagnetic signals, which is focused on protection and stealth rather than direct attack. Electromagnetic hardening involves reinforcing or protecting systems against threats from electromagnetic interference, aimed at maintaining system integrity rather than attacking enemy systems. Frequency agility in radar systems pertains to the ability to rapidly switch frequencies to avoid detection or interference, mainly as a defensive tactic rather than a straightforward offensive electronic attack.