Facts: Garrett Greller wants to sell a pain reliever made with CBD oil, a cannabis extract. Greller wants to know if CBD oil is considered a "controlled substance" under the Federal Controlled Substances Act. If so, it would be illegal to sell. Greller searched and found the following decisions: Allen v. US, where a U.S. District Court in Indiana ruled that CBD oil is illegal, a decision that was not appealed to the Seventh Circuit Court of Appeals (which reviews decisions by courts in Indiana, Illinois, and Wisconsin). Beck v. US, where a U.S. District Court in Michigan ruled that CBD oil is legal, and on appeal the Sixth Circuit Court of Appeals (which reviews decisions by courts in Michigan, Ohio, Kentucky, and Tennessee) reversed that decision. Clark v. US, where a U.S. District Court in Wisconsin ruled that CBD oil is illegal, and on appeal the Seventh Circuit Court of Appeals (which reviews decisions by courts in Indiana, Illinois, and Wisconsin) reversed that decision. Dale v. US, where a U.S. District Court in Texas ruled that CBD oil is legal, a decision that was not appealed to the Fifth Circuit Court of Appeals (which reviews decisions by courts in Texas, Mississippi, and Louisiana).

After doing business for six months, Greller sold 50% of his business to his friend Klein (who became a co-owner). Based solely on these facts, what was the legal form of Greller and Klein's business?

A. Limited partnership B. Sole proprietorship C. Corporation D. General partnership E. Limited Liability Company