You can use a standard caterers symbol, as a chef's hat, on your business card as your

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.