Question: A scientist studied a species of fish. She found that when a certain nutrient was added to the diet of the fish just after hatching, the fish gained an average of 3 kilograms in the first year. What additional information is needed to determine whether the nutrient is affecting the growth of the fish?

  Options: 
 A. how much adult fish gained on average when the same nutrient was added to their diet
 B. how much newly hatched fish in this species gain in the first year without the nutrient in their diet
 C. how much of the nutrient is available for the fish species in their natural surroundings
 D. how much other species of fish gain in the first year when the nutrient is added to their diet
Answer: B