The Difference Between the Schemes of Substage 3 Infants and Substage

The difference between the schemes of substage 3 infants and substage 4 infants is that

A) substage 3 infants use schemes for the pleasure of using them, whereas substage 4 infants use schemes to explore the environment.
B) the schemes of substage 3 infants are limited to single sensory modalities whereas the schemes of substage 4 infants involve the coordination of input from more than one modality.
C) substage 3 infants can reproduce activities they happen upon by chance, whereas substage 4 infants can employ means-ends analysis to produce a desired effect.
D) when trying to solve problems, substage 3 infants use initially successful solutions repeatedly, whereas substage 4 infants engage in active trial and error.