Respuesta :
It's c) Tracking the temp. in a city over a five year period.
*notice it's the only question with a note of how long they observe for*
Answer:
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