Siegler's Overlapping Waves Model Represents the Fact That

Siegler's overlapping waves model represents the fact that

A) different children, each of whom represents a wave, have different but overlapping waves of ability.
B) more than one strategy is available to solve arithmetic problems, and each strategy is used to a different degree at different points in one's development.
C) arithmetic ability is distributed like wave, and different age groups will have different crests.
D) older children may ebb and flow in their use of higher level arithmetic strategies.