Concept:Developmental tasks are age-specific challenges that a person must master to progress normally through life.Explanation:Robert Havighurst introduced the idea of developmental tasks in 1950.He stated that at each life stage, society expects certain achievements (e.g., a child must study, a parent must support the family).These tasks arise predictably and must be completed for healthy development.Thus, Havighurst is the psychologist who proposed the concept.Answer:B. Havighurst