Which of the following best describe implementation challenges that are associated with variablelength numbering plans?

A.
the variable number of extensions that need to be implemented

B.
the number of trunks that need to be assigned

C.
the mapping between IP addresses and extension numbers

D.
the identification of the number of digits that need to be dialed before the call is routed

E.
the degree in which the dial plan varies.

Explanation:
Explanation- An open numbering plan, as found in countries that have not yet standardized on
numbering plans, features variance in the length of the area code or the local number, or both.
Link-http://www.ciscopress.com/articles/article.asp?p=1715059