c. Giraffes that stretch their necks more than other giraffes will have babies with longer necks.
Explanation:
Giraffes that stretch their necks will not have babies with longer necks. A trait only shows in next generation if it is genetically inherited i.e. the gametes carry the trait to the next generation.
When giraffes stretch their necks, they are modifying their actions in their life time which will have no effect on the gametes. Hence, this trait wont be passed to the next generation and babies will not have longer necks.
B. a volcano that erupts in blasts of the pyroclastic matter. D. would be wrong because the shield volcano can have explosive eruptions but they are generally quiet