The correct answer is A.
OBJ-1.6: Zero-day attacks have no known fix, so patches will not correct them. A zero-day vulnerability is a computer-software vulnerability that is unknown to, or unaddressed by, those who should be interested in mitigating the vulnerability (including the vendor of the target software). If a discovered software bug or known vulnerability is found, a patch or mitigation is normally available. If a piece of malware has well-defined indicators of compromise, a patch or signature can be created to defend against it, as well.