What is that sweet and sour flavored sauce that comes with the chicken nuggets you buy at McDonald's:

Sweet and spicy sauce, sweet and sour sauce.

McDonald's buy chicken nuggets to send that sweet and sour flavor of the sauce is an extension of what sauce:

McDonald's restaurant (McDonald's Corporation) 1940 by the McDonald brothers and Ray Kroc in the United States founded a large chain of fast-food group. McDonald's is headquartered in Oakbrook, Illinois, the United States, in the world has about 30,000 stores, with a total investment of 500 million U.S. dollars, mainly selling hamburgers, French fries, fried chicken, soda, salads. McDonald's restaurants are located in more than 100 countries on six continents, and in many countries McDonald's represents an American way of life. McDonald's in mainland China in the early translation of the name is "McDonald's fast food". October 8, 1990, the first McDonald's restaurant in mainland China opened in Shenzhen. October 12, 2017, McDonald's (China) Ltd. officially changed its name to the golden arches of the (China) Ltd.