Which of the following statements is valid about generic procedures in C#.NET?

Which of the following statements are valid about generics in .NET Framework?

1. Generics is a language feature.
2. We can create a generic class, however, we cannot create a generic interface in C#.NET.
3. Generics delegates are not allowed in C#.NET.
4. Generics are useful in collection classes in .NET framework.
5. None of the above

For the code snippet shown below, which of the following statements are valid?

public class Generic<T>
{
    public T Field; 
    public void TestSub()
    {
        T i = Field + 1;
    }
}
class MyProgram
{
    static void Main(string[] args)
    {
        Generic<int> gen = new Generic<int>();
        gen.TestSub();
    }
}

Which one of the following classes are present System.Collections.Generic namespace?

1. Stack
2. Tree
3. SortedDictionary
4. SortedArray