Final answer:
The Harvard Grant Study is one of the best known and enduring studies of adolescents in the US, providing valuable insights into human development and factors that influence success and happiness.
Step-by-step explanation:
One of the best known and enduring studies of adolescents in the US is the Harvard Grant Study. This study began in 1938 and followed a group of male Harvard students for over 80 years, examining various aspects of their lives including physical and mental health, relationships, careers, and overall well-being. The study has provided valuable insights into human development and has contributed to our understanding of factors that influence success and happiness in life.