A. 1973
B. 1971
C. 1972
D. None of these

Explanation: The Strategic Arms Limitation Treaty (SALT-I) was signed on May 26, 1972, between the United States and the Soviet Union to limit the number of nuclear arms. The years 1971 and 1973 are incorrect, and “None of these” is thus not applicable.

The correct answer to the question: "The Strategic Arms Limitation Treaty (SALT-I) was signed in:" is "1972".