Only variables (answer E) cannot be encapsulated by a namespace. They can be declared within a namespace but they will become part of the global scope and not of the namespace. So if you need to access a variable that was decared in a namespace look in global scope.
A note on constants. Those declared using const can be part of namespaces, those declared using define() cannot. However the latter can be made to look like that they are part of a namespace by using tricks as:
Now the namespace is part of the constant name and you can reference it using namespace syntax. But it's faked so you can't use aliases for instance.