Those who are in favor of bringing the wolves back to Yellowstone have their arguments. Biologists say that wolves 41 an important part in the ecosystem of this wilderness area. Through their 42 they remove the weak and diseased members of the elk and deer populations. They keep the population 43 growing too large. Naturalists believe the wolves are an essential part of the wilderness. And they are the only part of the ecosystem that is 44 from the Yellowstone area. Naturalists want to restore Yellowstone to the way it 45 before Columbus set foot in America in 1492. They want visitors to the park to have the experience of hearing wolves howl at night—an experience many describe as the best the wilderness has to offer.
【題組】45 (A) is (B) was (C) were (D) has been