A small business just recovered from a ransomware attack against its file servers by purchasing the decryption keys from the attackers. The issue was triggered by a phishing email and the IT administrator wants to ensure it does not happen again. Which of the following should the IT administrator do FIRST after recovery? 

Answer options:

A. Scan the NAS for residual or dormant malware and take new daily backups that are tested on a frequent basis.
B. Restrict administrative privileges and patch all systems and applications.
C. Rebuild all workstations and install new antivirus software.
D. Implement application whitelisting and perform user application hardening.

A