Reza: Language requires the use of verbal signs for objects as well as for feelings. Many animals can vocally express hunger, but only humans can ask for an egg or an apple by naming it. And using verbal signs for objects requires the ability to distinguish these objects from other objects, which in turn requires conceptual thought. If all of Reza's statements are true, then which one of the following must also be true? ['All humans are capable of conceptual thought.', 'Conceptual thought requires the use of verbal signs for objects.', 'Conceptual thought is required for language.', 'The vocal expressions of animals other than humans do not require conceptual thought.']