Here's a problem to solve: Students are performing an investigation to determine the types of bacteria that grow inside their school. Which activity should the students avoid while performing this investigation?

Among the 4 following options, which is the correct answer?

- A: wearing gloves while handling the samples
 
- B: cleaning all materials they have finished using
 
- C: bringing food and drinks into the laboratory
 
- D: washing hands before leaving the laboratory
 