In which cases were tax cuts followed by robust growth?

a. the ones of the Kennedy administration in 1964 and the ones of the Reagan administration in 1981
b. the ones of the Kennedy administration in 1964 but not the ones of the Reagan administration in 1981
c. the ones of the Reagan administration in 1981 but not the ones of the Kennedy administration in 1964
d. neither the ones of the Kennedy administration in 1964 nor the ones of the Reagan administration in 1981

a