Derived class method without matching base class method?

Question

I would like to have methods that are unique to a sub-class. Visual Studio doesn't like this and won't let me compile. Is it possible to have a method in a derived class without it being in the base? Consider the following pseudocode:

 

abstract Class Vehicle
  Vehicle()

Class Car : Vehicle
  Car()
  OpenTop(bool isConvertible)

Class Truck : Vehicle
  Truck()
  PullTrailer(bool hasTrailerHitch)

Main
  Vehicle car = new Car();
  Vehicle truck = new Truck();

  car.OpenTop(true);  // It doesn't like this.
  car.PullTrailer(false); // Or this.

From the error it looks like the program expects both OpenTop and PullTrailer to appear in Vehicle, which I could, but I believe that I have been able to do something similar to this in past code, so I'm not sure what I'm missing. Must I declare the car and truck as:

 

Car car = new Car();

and

Truck truck = new Truck();

 

And if I do that, will it prevent me from using anything from Vehicle?