The correct answer is - the first object, the animal skull.
The radiocarbon dating, also referred to as carbon -14 dating, is used for the determining of the age of an object containing organic matter based on the properties of the radiocarbon.
By using this method, the scientists can relatively accurately determine the age of an object from the past. Still this method is restricted, as it can only determine the age of an object that contains organic matter, otherwise it will not have any relevant effect.
In this picture, the only object that contains organic material is the animal skull, thus it is the only one that can be dated with this method. The second picture represents a fossil of a plant, but only as a print, so no organic matter there, while the third one is a rock.