Answer:
The correct answer is option 3. tracking the temperature in a city over a five year period.
Explanation:
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An observational study is a study in which observations are made and conclusions are drawn from them.
In the case of the options given, an observational study is that of option 3. tracking the temperature in a city over a five year period, since for five years we will carry out measurements and observations of the temperature to obtain some conclusion.
We conclude that the correct answer is option 3. tracking the temperature in a city over a five year period.
