YA novel #5 - The exchange student by Kate Gilmore

This novel is about a girl whose parents sign up for an exchange student from another planet. This is set in the future after the world has been annihilated by a ecological catastrophe. The heroine is involved in rebreeding all of the animals on earth. All the common sci-fi stuff is there, food replicators, etc. her exchange student eats a lot, turns colors according to his mood and is very interested in the animals. their relationship develops but she can tell that there is something she is not telling him. Great story, good sci-fi background. a little slow, but most sci-fi novels are, aren't they?