Answer: A)APT (Advanced persistent threat)
Explanation: APT(Advanced persistent threat)is the exploitation of the system which gets notice after a long period of time and remains undetected till then. The unauthorized measure is taken to sneaks into any particular network and then hack that network .
Other options are incorrect because zero day threat is the attack that occurs the same day the vulnerability is detected. ,false positive is the outcome that is gained due to incorrect information and DoS (Denial of service) is the attack that produce compromised system due to loading the system with malware.
Thus, the correct option is option(A).