How to access the base class values in derived class?

Hi All,
Can any one let me know "How to access the base class values in derived class"?
For Example:

public class A     {         public int a = 5;
public string ReturnString()
{
//Do Something
} }
Class B : A
{
Public void SetValues()
{
//How do I access the value of a here?
}
}
 
...