As the willow trees release compounds that can help other trees be well prepared for an insect attack, the addition of those trees surrounding the orchard would be helpful because the insects would have to pass through them before reaching the orchids. Then, the trees would release the compound and the other plants would be "warned" about the danger, including the orchids. Therefore, the correct answer is:
B.The willow trees will function as an alarm system, warning the fruit trees if tree-cating insects are encroaching from the forest, so that they can be better prepared to survive an attack