D
Below is a question with multiple-choice answers. Choose the correct option based on your reasoning.

### Question:
A farmer wants to know if adding fertilizer to his field will make his crops healthier. Which activity should the farmer do first?

### Choices:
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.

### Answer:
