Of the following, which one is an observational study?

1. asking people for their opinion on the taste of a new cereal
2. checking the effectiveness of a new headache medicine by giving one group the new medicine and one group acetaminophen
3. tracking the temperature in a city over a five year period
4. measuring the average strength of a batch of metal by stressing some sample pieces until they deform

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.

explanation:

for  example, forests have higher evapotranspiration than other ecosystems,  such  as grasslands, because of their deeper roots and greater leaf area. thus forests have a net moistening effect on the atmosphere and become a moisture source for downwind ecosystems.

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