In the Once-ler's opinion, what must happen for the Lorax and other animals to be able to return?
a) The Truffula trees must be replanted and allowed to grow.
b) The Once-ler must apologize to the Lorax and the animals.
c) The polluted air and water must be cleaned and restored.
d) The Once-ler believes the Lorax and other animals can never return.