10.3.3 Inheritance
A class inherits the members of its direct base class type. Inheritance means that a class implicitly contains all members of its direct base class type, except for the instance constructors, destructors and static constructors of the base class.

class Program
{
  static void Main(string[] args)
  {
    Console.WriteLine(B._str);
  }
}

class A
{
  public static string _str = "test";
}

class B: A {}

Console.WriteLine(A._str);

10.12 Static constructors
...
The execution of a static constructor is triggered by the first of the following events to occur within an application domain:
• An instance of the class type is created.
• Any of the static members of the class type are referenced.

public class A
{
  public static string str = Init();

  public static void Yell()
  {
    Console.WriteLine(">> Yell");
  }

  private static string Init()
  {
    return ">> Init";
  }

  static A()
  {
  }
}

public class EntryPoint
{
  static void Main()
  {
    A.Yell();
  }
}

>> Yell

BIS>  private static string Init()
BIS>  {
BIS>    return ">> Init";
BIS>  }

private static string Init()
{
    Console.WriteLine(">> Init");
    return ">> Init";
}