Final answer:
Cognitive Development is the correct answer to the question, as it refers to the growth in humans' ability to think in increasingly complex ways and is a primary focus of developmental psychologists.
Step-by-step explanation:
The question refers to the growth in humans' ability to think in increasingly complex ways, and the correct option is a) Cognitive Development. Cognitive development is a significant domain in the field of developmental psychology, which encompasses learning, attention, memory, language, thinking, reasoning, and creativity.
Notably, during adolescence, individuals transition to formal operational thought, a phase characterized by the capability for abstract reasoning, considering multiple viewpoints, forming new ideas, and engaging in hypothetical thinking. Additionally, cognitive development is not restricted to any single life stage but continues actively throughout one's lifespan.
Developmental psychologists emphasize that this development occurs across three domains: physical, cognitive, and psychosocial, with the latter involving emotions, personality, and social relationships. Hence, consistent with the provided references, cognitive development truly captures the essence of humans' progression in complex thinking ability.