Here's a problem to solve: A farmer wants to know if adding fertilizer to his field will make his crops healthier. Which activity should the farmer do first?

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

- A: Plant different crops in a nearby fertilized field.
 
- B: Water the crops in the field before adding fertilizers.
 
- C: Add many different fertilizers to the field at once.
 
- D: Record the appearance of the crops before fertilizing.
 