Multiple Inheritance in C#
Does C# support multiple Inheritance ?
No, you cannot inherit from multiple classes. You may use interfaces or a combination of one class and interface(s).
More about.....Multiple inheritance in C#
How do you prevent a class from being inherited ?

In C# you can use the "sealed" keyword in order to prevent a class from being inherited. If you try to attempts to inherit will result in a compilation error.
In VB.Net you can use "NotInheritable" (NonOverrideable for properties)
Also in Java you can use the keyword "final"
More about.....Sealed Classes
Explain namespaces in C# ?

Namespaces are containers that is used to declare a scope that contains a set of related objects. You can use a namespace to organize code elements and to create globally unique types.
Within a namespace, you can declare another namespace, class, interface, struct, enum, and delegates.
Ex:
More about......Net namespaces
How do you convert a value-type to a reference-type ?
You can use Boxing.
What is boxing and unboxing ?
Implicit conversion of value type to reference type of a variable is known as boxing and conversion of reference type variable back to value type is called as UnBoxing.
Ex:
More about.....Boxing and Unboxing