Final answer:
Teaching creation-science and evolution-science together is not allowed in public schools due to court rulings and the Establishment Clause of the First Amendment. Alternative theories lack scientific usefulness and teaching them as science is against the law.
Step-by-step explanation:
Teaching creation-science and evolution-science together is not allowed in public schools based on court rulings. This is because teaching alternative theories to evolution, such as creation-science, is considered a violation of the Establishment Clause of the First Amendment of the U.S. Constitution. The court rulings have determined that alternative theories lack scientific usefulness and are not scientific explanations. Furthermore, teaching these theories as science is against the law in the United States.