What is the nature of the method used to escalate issue very serious ?

[PlAwAnSaI]

According to the ITILv3 framework, what is the nature of the method used to escalate an issue that is very serious in nature or an issue that could potentially require an excessive amount of time to resolve?

A. both hierarchical and functional
B. both conceptual and procedural
C. both hierarchical and procedural
D. both conceptual and functional