What was reagan's strategic defense initiative?

a. an agreement the u. s. signed with the ussr to destroy their nuclear arsenals over fifty years
b. a shield of missiles over the u. s. designed to shoot down incoming nuclear missiles from the ussr
c. an agreement the u. s. made with the ussr to make sure no other country would get a nuclear weapon
d. a plan to invade cuba so the soviets could never directly attack the united states