A. 1948
B. 1949
C. 1950
D. None of these

Explanation: The North Atlantic Treaty Organization (NATO) was established on April 4, 1949, as a collective defense alliance during the early Cold War. The years 1948 and 1950 are incorrect, and “None of these” is thus not applicable.

The correct answer to the question: "NATO was formed in:" is "1949".