In a attack, the attacker sends a large number of connection or information requests to disrupt a target from many locations at the same time.

DDoS - Distributed Denial of Service

Explanation:

In DDoS attack, the attack comes from various system to a particular one by making some internet traffic. This attack is initiated from various compromised devices, sometimes distributed globally through a botnet. It is different from other attacks  such as (DoS) Denial of Service attacks, in which it utilizes an unique Internet-connected device ( single network connection) to stream a target with the malicious traffic. So in DDoS, multiple systems are involved in the attack and hence we can conclude that as the answer.

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The correct answer to go in the blank would be a) complement.