What is the significance of hadrian 's wall? the wall was a monument to fallen roman soldiers. the wall marked the boundary between ancient greece and rome. the wall was built as a temporary structure but lasted hundreds of years. the wall marked the northern defensive boundary of roman britain.

D.The wall marked the northern defensive boundary of Roman Britain.

D. Observational study

Step-by-step explanation:

We are given that Nico looked around the cafeteria during the lunch to see whether people purchased lunch or brought their own.

It is known that:

1. 'Survey' means to question a wide variety of population about their views on a particular issue.

2. 'Simulation' refers to act out a situation or process in order to find some conclusions.

3. 'Experiment' represent a scientific procedure undertaken in demonstrate a fact or test a hypothesis.

4. 'Observational study' is to study the samples without the variables being under the control of the observer.