Get list of properties from List of objects
LINQ is the answer. You can use it to "project" from your object collection to another collection - in this case a collection of object property values.
List<string> properties = objectList.Select(o => o.StringProperty).ToList();
You could use LINQ:
List<X> Z = GetXlist();
List<String> r = Z.Select(z => z.A).ToList();
return r;
Or just,
return GetXlist().Select(z => z.A).ToList();
Find out more about LINQ. It is pretty useful.