What does artificial selection in high-milk-yielding cows indicate?

• A
  Stabilizing selection that stabilizes this trait in the population.
• B
  Directional selection that pushes the mean of the trait in one direction.
• C
  Disruptive selection that splits the population into two, one high-yielding and one low-yielding.
• D
  Stabilizing selection followed by disruptive selection that splits the population into high-yielding cows.