Final answer:
The researcher's area of interest is cholesterol levels. They want to study the cholesterol levels of adults in the city.
Step-by-step explanation:
The researcher's area of interest is 1) Cholesterol levels. The researcher wants to study the cholesterol levels of adults in the city. Cholesterol levels are an important factor when assessing the risk of heart disease, so understanding the distribution of cholesterol levels in adults can provide valuable insights for public health and medical interventions.