Question

which method of gathering data will be most effective in learning how diet and fitness choices affect long - term health?
an experiment
an observational study
a sample survey
a census

Explanation:

To determine how diet and fitness choices affect long - term health, an observational study is most effective. An experiment would involve manipulating variables (like diet or fitness), but ethical and practical issues make it hard to control these factors over the long - term for a study on health. A sample survey or census would mainly gather self - reported data, which may not be as accurate or comprehensive for understanding the long - term health impacts of diet and fitness. In an observational study, we can observe people's natural diet and fitness behaviors over time and their corresponding health outcomes, making it suitable for this research question.

Answer:

an observational study