Of the following, which one is an observational study?

A Asking people for their opinion on the taste of a new cereal

B. Checking the effectiveness of a new headache medicine by giving one group the new medicine and one group acetaminophen

C. tracking the temperature in a city over a five year period

D. measuring the average strength of a batch of metal by stressing some sample pieces until they deform

Option c

Step-by-step explanation:

Observational study is the recording of data from observing the actual events happening without trying to control or manipulate it.

Example Recording temperature, humidity, heights of mountains at various places etc.

Asking people for their opinion about something would be a survey.

Option B is the study of comparison of two groups control group vs experiment group

Option C is right answer because this involves actual recording of the temperature over a five year period without any control or change

Option D is wrong because when we stress sample pieces we control something hence cannot be observational study