Final answer:
Crystallized intelligence and fluid intelligence are two aspects of cognitive development during young adulthood.
Step-by-step explanation:
Two aspects of cognitive development that occur during young adulthood are crystallized intelligence and fluid intelligence. Crystallized intelligence refers to the accumulation of knowledge and skills gained through experience and education. It includes things like vocabulary, general knowledge, and expertise in specific domains. Fluid intelligence, on the other hand, refers to the ability to think abstractly, solve novel problems, and adapt to new situations. It involves processes such as reasoning, memory, and information processing.