Which of the following statements is correct about a namespace in C#.NET?

• Namespaces help us to control the visibility of the elements present in it.
• A namespace can contain a class but not another namespace.
• If not mentioned, then the name 'root' gets assigned to the namespace.
• It is necessary to use the using statement to be able to use an element of a namespace.
• We need to organise the classes declared in Framework Class Library into different namespaces.