An extension method is a static method that extends an existing class or data type.

An extension method can only have one parameter.

Inheritance involves a base class and a relative class.

If two methods have the same names and parameter lists, you cannot overload them by just giving them different return types.

A method can return a primitive value or a struct object, but it cannot return an object that is an instance of a class.

The following statement will cause a compiler error:int number = null;

In code that creates an instance of a class, you access the class object’s properties in the same way that you would access public variables.

Constructors cannot accept arguments in the same way as other methods.

To make a property read-only, you must omit the get accessor for the property.

A class is not an object; it is a description of an object.