1.  
  2. public class Child : Person
  3. {
  4. private static int maximumAge;
  5. public Child(string lastName, string firstName) : base(lastName, firstName)
  6. { }
  7.  
  8. static Child() => maximumAge = 18;
  9.  
  10. // Remaining implementation of Child class.
  11. }
  12.