Which of the Following Would Be an Asymmetric Alliance

Which of the following would be an asymmetric alliance?

A) The de facto agreement between the United States and the Soviet Union not to use nuclear weapons
B) The Cold War weapons agreements that allowed the Soviet Union to keep more nuclear missiles than the United States
C) The United States pledging to defend Costa Rica if that country is attacked
D) The agreement between France and Russia before World War II to come to each other's aid