Final answer:
The only foreign enterprise that Shah Muhammad Reza Pahlavi could not control was the Anglo-Iranian Oil Company, now known as British Petroleum (BP), due to the company's establishment by the British government in Iran's oil industry and sustained through political support by both the US and UK.
Step-by-step explanation:
The foreign enterprise that Shah Muhammad Reza Pahlavi of Iran could not control was the Anglo-Iranian Oil Company, known today as British Petroleum (BP). This was due to the fact that during the early part of the 20th century, the British had established a significant foothold in Iran's oil industry through the founding of the Anglo-Persian Oil Company in 1908, which controlled oil production in Iran. Despite efforts by Prime Minister Muhammad Mossadeq to nationalize Iran's oil fields, US and British business interests, through political maneuvering and covert operations, ensured the Shah remained in power and foreign involvement in Iran's oil industry continued.