Im not sure which one it is

In shifting to a defense policy based upon the concept of "flexible response," president kennedy was indicating that he had grave doubts about thevalue of which previous defense policy? a massive retaliationb collective securityc containmentd air power

Ascientist performs an experiment where she measures the mass of a piece of metal, pours acid onto the metal, washes the metal, and then re-measures the mass of the metal. the scientist repeats the experiment several times, each time increasing the amount of acid used. the dependent variable in the experiment is the: initial mass of the metal final mass of the metal amount of acid used washing the metal

What does it mean to say the united states has a federal system of government