Aresearch study examined the intellectual growth of 20 premature children over a period of 18 years. this is best described as an example of . naturalistic observation
2. a longitudinal study
3. a case study
4. a cross-sectional study

2). A Longitudinal study

Explanation:

Longitudinal Study or research is a type of observational research (study) in which specific subjects (variables) are observed and data is gathered on them over a period of time. In this case, the subjects being observed are the premature children, the data collected on them are their intellectual growth and this research was carried out over the period of Eighteen (18) years.

i believe the answer would be negative peer pressure