单选题 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 email 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.

【正确答案】 D

【答案解析】在“And on top of the realities listed above，security managers are being asked to support increasing degrees of network availability and access．”这一句中，“top”的意思就是“the most important”，所以正确答案应为D。