Final answer:
The correct option is a. Sensorimotor play.
The 'getting into everything' behavior of 1-year-olds as described by Piaget is referred to as sensorimotor play, a developmental stage where infants interact with the world through their senses and actions to learn and grow cognitively.
Step-by-step explanation:
The "getting into everything" activities of 1-year-olds referred to in Piaget's theory of cognitive development is known as sensorimotor play. This stage is characterized by the exploration of the world through the senses and motor behavior. During the sensorimotor stage, which lasts from birth to about 2 years old, infants learn about their surroundings by interacting with it directly.
They may put objects in their mouths or shake and bang things to see if they produce sounds. This stage is foundational in developing cognitive abilities such as object permanence. It is a period where children assimilate new information and experiences into their current mental models and accommodate their existing schemata based on interactions with the environment.