Which of the following statements represents a difference between a sample survey and an observational study? A) Presence of population. B) Inclusion of numerical data. C) People are aware that they are participating. D) Ability to collect information.

Answer: C) People are aware that they are participating.

The sample survey is the technique which is initiates after taking proper consent from the participants by explaining the purpose of study and then data is collected which can be in the form of output of measurements, opinion about a cause or issue. But the observational study does not explain the purpose of the study to the participants, it just involves the data collection.

Therefore, on the basis of the above description, People are aware that they are participating. is the relevant option.

c seems most likely from the given answers