A) he approved a U.S. military strike against Afghanistan
B) he blocked food shipments to the Soviets and announced a U.S. boycott of the Olympic games
C) he blockaded Soviet port cities
D) he negotiated a peace treaty between the Soviets and Afgans
Of the answers that you have given us, the only possible correct answer is B. None of the others is true.
In December of 1979, the Soviet Union invaded Afghanistan in an attempt to prop up the Afghan government, which was a communist regime. The US felt that this invasion was simply not acceptable. However, the US was not willing to go to war with the Soviet Union over Afghanistan. For this reason, Carter did not try to take military actions such as those mentioned in A and C.
Instead, Carter tried to use other means of exerting pressure on the Soviets. As the eNotes link below says,
Carter responded by withdrawing SALT II from Senate consideration, halting grain sales to the Soviet Union, urging a boycott of the Olympic Games in Moscow, and asking for a large increase in military spending.