Option A, online school sales of books and courses belong to part-time business, and they are not subordinate, belonging to non-VAT taxable services; Option b, the sales of doors and windows are within the scope of value-added tax, and the installation of doors and windows is within the scope of business tax, which belongs to non-VAT taxable services for different customers; Option c, the restaurant sells tobacco and alcohol to customers while providing catering services, which belongs to the mixed sales of business tax, and the business tax is calculated and paid according to the main business; Option D, providing interior decoration belongs to the scope of business tax, and selling cars and providing interior decoration services are also aimed at the same customer, which belongs to mixed sales and should be subject to value-added tax.