Which of the following is less vulnerable to threats and attacks because it is not associated with one specific operating system？（）

A.by enabling business to leverage investments in the network
B.by spending less time addressing attacks
C.by enforcing policy compliance
D.through admission control

A.intense competition that is driven by the increased number of discounters
B.declining customer loyalty
C.compensating for staff shortages
D.changes in demographics
E.high operating costs
F.desire to offer Internet access in stores

A.plan
B.design
C.implement
D.prepare