An administrator wants to be alerted when a network-based attack is underway but the company policy prohibits blocking or dropping network connections.Which of the following MUST be deployed?()

An administrator wants to be alerted when a network-based attack is underway, but the company policy prohibits blocking or dropping network connections.Which of the following MUST be deployed？（）

A、IDS

B、IPS

C、Firewall

D、Managed PKI