The most likely approach to be used in studying the reasoning abilities of adolescence is the cognitive approach.
The cognitive approach focuses on how individuals perceive, process, and use information to reason, solve problems, and make decisions. It is concerned with the mental processes involved in thinking, such as attention, perception, memory, and decision-making. This approach is particularly relevant to studying the reasoning abilities of adolescents, as it provides a framework for understanding how their cognitive abilities develop and change during adolescence.
The behaviorist approach is focused on observable behavior and the environmental factors that influence it, and is less relevant to studying the internal mental processes involved in reasoning. The constructivist approach emphasizes the role of individual experience and construction of meaning, but may not provide as clear a framework for studying reasoning abilities as the cognitive approach. The humanistic approach is focused on personal growth, self-actualization, and subjective experience, and is not directly related to studying reasoning abilities.
Therefore, the correct answer is the cognitive approach.