Deena used to think that everyone else liked the same people she liked. She now realizes that different people may have different opinions toward others. Piaget would suggest that Deena has recently become a thinker.

concrete operational        

Explanation:

The concrete-operational stage is described as the third stage in the 'cognitive development theory' which was introduced by Jean Piaget. The given period starts with the age of seven and last till eleven years of age i.e, in the middle childhood and is distinguished by a child's development of 'logical thought' or 'reasoning' related to the real-life situations in the absence of any changes in the appearances.

A concrete-operational thinker is a person who falls under the third stage of cognitive development.

Piaget would suggest that Deena has recently become a concrete-operational thinker.