What is a primary difference between the OECD and UN model tax treaties? O a. The UN model assumes all countries are economic equals, whereas the OECD model does not. O b. All of the above are differences between the OECD and UN models. O c. The UN model grants more taxing rights to the host country than does the OECD model when host country is developing countries. O d. The model treaty of the UN gives more taxing rights to well-developed countries than x developing countries