Leonard is teaching Sally how to play a new card game. During the first time through the game, Leonard looks at Sally's cards and helps her decide how to play them at each turn. As Sally becomes more familiar with the game's rules and strategies, Leonard gives her fewer hints and less assistance. This scenario best illustrates:_______.
A. Scaffolding.
B. Equilibration.
C. Dis-equilibrium.
D. Social constructivism.