Artificial selection to obtain cows yielding higher milk output represents:

• A
  directional selection as it pushes the mean of the character in one direction.
• B
  disruptive selection as it splits the population into two,one yielding higher output and the other lower output.
• C
  stabilising followed by disruptive as it stabilises the population to produce higher yielding cows.
• D
  stabilising selection as it stabilises this character in the population.