Answer:
The factor that best explains the availability of these foods in U.S. grocery stores is A, the influence of ethnic groups on the diet of U.S. consumers.
Each of the food pairings mentioned is associated with a specific ethnic cuisine:
Refried beans and tortillas are commonly found in Mexican cuisine
Sauerkraut and bratwurst are commonly found in German cuisine
Soy sauce and fried rice are commonly found in Asian cuisine, particularly Chinese and Japanese cuisine
Hummus and pita bread are commonly found in Middle Eastern cuisine
The availability of these foods in U.S. grocery stores can be attributed to the influence of the immigrant populations from these countries, as well as the growing interest and appreciation of diverse cultural cuisines by U.S. consumers. Therefore, option A, the influence of ethnic groups on the diet of U.S. consumers, is the best explanation for the availability of these foods in U.S. grocery stores.