4. how will the amount of fertilizer used on a field affect the number of earth - worms found there…

Explanation:

Step1: Identify constant/control variables

Constants could be factors like type of soil, temperature, amount of sunlight the field receives, etc. These are kept the same so that only the amount of fertilizer affects the number of earth - worms. Constant/Control Variables: Type of soil, temperature, amount of sunlight

Step2: Formulate hypothesis

A possible hypothesis could be that as the amount of fertilizer increases, the number of earth - worms will initially increase up to a certain point due to improved soil conditions, but then decrease as excessive fertilizer can be harmful. Hypothesis/Prediction: As the amount of fertilizer used on a field increases, the number of earth - worms will initially increase, but after a certain amount, the number of earth - worms will decrease due to potential toxicity of excessive fertilizer.

Answer:

Constant/Control Variables: Type of soil, temperature, amount of sunlight Hypothesis/Prediction: As the amount of fertilizer used on a field increases, the number of earth - worms will initially increase, but after a certain amount, the number of earth - worms will decrease due to potential toxicity of excessive fertilizer.