The answer is d. the continual stretching of giraffe's necks to reach leaves led to longer necks.
Explanation:
This statement was one of the main ideas of Lamarck's proposal inheritance. He thought that as giraffes needed to elongate their necks in order to reach the higher parts of the trees, then, the necks actually elongated. So the need was prior to the mutation. We now know that mutations happen before the change in the whole population.
