Jean Piaget believed that knowledge is :

Piaget's theory of cognitive development is a constructivist account: he held that children are not passive recipients of knowledge from the environment, nor is knowledge simply innate. Instead, children actively construct their own understanding by acting on and interacting with the world, continually building and revising internal mental structures called schemas through the twin processes of assimilation (fitting new experience into existing schemas) and accommodation (modifying schemas when experience does not fit).

In the stem, only one option captures this: knowledge described as constructed by the child through interaction with the environment, rather than passed passively from it. This directly states Piaget's constructivist claim, so it is the correct description of what Piaget believed.

Contrast with the other options:

• Knowledge as innate and given, acquired without interaction, describes nativism -- a different position that denies experience plays a formative role, which conflicts with Piaget's insistence that a child's own activity is what drives development.

• Knowledge as co-constructed with more knowledgeable others describes Lev Vygotsky's socio-cultural theory, which foregrounds guided social interaction (e.g. within the Zone of Proximal Development) -- a genuinely different theorist's framework, not Piaget's account of the child's own individual engagement with the physical world.

• Knowledge as a visible, reliably measurable behavioural change describes behaviourism, which is concerned only with observable behaviour and explicitly sets aside internal mental activity -- the opposite emphasis to Piaget's cognitive, structure-building account.

Hence Piaget's own position is best captured by the option describing knowledge as actively constructed by the child through interaction with the environment.