In Terms of Piaget's Stages of Sensorimotor Development, at What

In terms of Piaget's stages of Sensorimotor Development, at what age would you expect to see evidence of an infant reaching the substage of tertiary circular reactions?

A) 1-4 months - when an infant can gain control over reflex behaviours
B) 8-12 months - when an infant is able to repeat chance behaviours which lead to satisfactory results and may be able to anticipate events
C) 12-18 months - when the infant repeats actions, varying them deliberately in an exploratory manner
D) 18-24 months - when the concept of 'pretend play' begins to develop