You design a Business Intelligence (BI) solution by using SQL Server 2008. The instance contains an SQL Server 2008 Analysis Services (SSAS) database. The SSAS database contains a cube named Sales. The Sales cube has a dimension named Geography and a role named roleEurope.
The Geography dimension has a hierarchy that contains the following members:
-Continent
-Region
-City

You plan to design the security configuration for the Sales cube. You need to enable the Read permissions for the roleEurope role. You also need to ensure that the roleEurope role can access only the Fact rows that are members of the Europe continent. Which Multidimensional Expressions (MDX) statement should you use?

A.
MEASURES.CURRENTMEMBER IS EUROPE

B.
MEASURES.CURRENTMEMBER[CONTINENT] IS EUROPE

C.
ANCESTOR(GEOGRAPHY.CURRENTMEMBER) IS EUROPE

D.
ANCESTOR(GEOGRAPHY.CURRENTMEMBER,[CONTINENT]) IS EUROPE

Explanation:
Tip: "security configuration … Multidimensional Expressions" = "ANCESTOR… [CONTINENT]"

The Ancestor function returns the parent, grandparent, great-grandparent, and so forth of the specified member. The Ancestor function requires two parameters, both of which must be placed within the parentheses. The first parameter is the member that serves as the starting point for the function. The second parameter is either the hierarchy level where the ancestor is to be found or an integer specifying the number of levels to move upward to find the ancestor.
(McGraw-Hill – Delivering Business Intelligence with Microsoft SQL Server 2008 (2009))

http://intelligent-bi.blogspot.com/2009/12/ancestor-mdx-function.html
http://technet.microsoft.com/en-us/library/ms145616.aspx
ANCESTOR MDX Function
A function that returns the ancestor of a specified member at a specified level or at a specified distance from the member.
Level syntax
Ancestor(Member_Expression, Level_Expression)
Member_Expression – A valid Multidimensional Expressions (MDX) expression that returns a member.
Level_Expression – A valid Multidimensional Expressions (MDX) expression that returns a level.