Dr. Smith is interested in how people change throughout their lives. She is particularly interested in how speech and language adapts and changes depending on a person's age. Dr. Smith is likely trained in what subfield of psychology?
developmental psychology

The answer is indeed developmental psychology.

Explanation:

Developmental psychology aims to study human change, growth, development, and consistency over the lifespan. It can approach several aspects of human life, such as biological, social, intellectual, perceptual, emotional, cognitive, physical, etc. Simply put, psychologists who specialize in this area - like Dr. Smith - wish to study how people change and grow, and what influences such change and growth.

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