প্রহেলিকা

The main goal of this research was to find out what factors make people's lives happier and healthier.
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Interesting fact:
Harvard University is conducting the longest-running research on adult development. This research involved 724 people and has been ongoing for 75 years. This research, which has been ongoing since before World War II, still has 60 active participants who are in their 90s.
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