Scientists have successfully cloned animals, including large mammals such as sheep. Which statement
provides the most likely reason that a human has not yet been cloned?
(1) Humans have DNA that is structurally very different from other mammals.
(2) Cloning can only be performed on animals that normally reproduce asexually.
(3) Human genes are made of too many different types of simple sugars.
(4) Some people consider human genetic experiments unethical.