Final answer:
The correct answer is option A. Formal operational.
Step-by-step explanation:
The stage of Piaget that has been found to not be achieved in some societies is the Formal operational stage.
Piaget's theory of cognitive development suggests that individuals progress through different stages of cognitive development as they grow. The formal operational stage is the final stage, which typically occurs during adolescence and into adulthood. This stage is characterized by the ability to think abstractly, reason logically, and engage in hypothetical thinking.
However, studies have shown that not all individuals in all societies reach the formal operational stage. Factors such as cultural differences, educational opportunities, and socioeconomic conditions can influence the achievement of this stage. Therefore, the formal operational stage may not be achieved in some societies.