题目内容：
What is the most important one among the realities listed? ________
A．New vulnerabilities will be introduced into your environment every day. B．If employees disregard warnings about the hazards of opening questionable e-mail attachments, the manager should educate them about properly configuring firewalls and intrusion detection systems for their PCs.
C．Managers have more responsibility than ever.
D．Security managers are asked to support increasing degrees of network availability and access.
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