At field sites around the world, Ken Dial saw a pattern in how young pheasants, quail, tinamous, and other ground birds ran along behind their  parents. "They jumped up like popcorn," he said, 5 describing how they would flap their half-formed wings and take short hops into the air. So when a group of graduate students challenged him to come up with new data on the age-old ground-up-tree-down debate, he designed a project10 to see what clues might lie in how baby game birds learned to fly.Ken settled on the Chukar Partridge as a model species, but he might not have made his discovery without a key piece of advice from the local15 rancher in Montana who was supplying him with birds. When the cowboy stopped by to see how things were going, Ken showed him his nice, tidy laboratory setup and explained how the birds' first hops and flights would be measured. The rancher20 was incredulous. "He took one look and said, in pretty colorful language, 'What are those birds doing on the ground? They hate to be on the ground! Give them something to climb on!" At first it seemed unnatural-ground birds don't like the ground? But25 as he thought about it Ken realized that all the species he'd watched in the wild preferred to rest on ledges, low branches, or other elevated perches where they were safe from predators. They really only used the ground for feeding and traveling. So he brought30 in some hay bales for the Chukars to perch on and then left his son in charge of feeding and data collection while he went away on a short work trip.Barely a teenager at the time, young Terry Dial was visibly upset when his father got back. "I asked 35 him how it went," Ken recalled, "and he said, 'Terrible! The birds are cheating!' " Instead of flying up to their perches, the baby Chukars were using their legs. Time and again Terry had watched them run right up the side of a hay bale, flapping all the40 while. Ken dashed out to see for himself, and that was the "aha" moment. "The birds were using their wings and legs cooperatively," he told me, and that single observation opened up a world of possibilities.Working together with Terry (who has since gone 45 on to study animal locomotion), Ken came up with a series of ingenious experiments, filming the birds as they raced up textured ramps tilted at increasing angles. As the incline increased, the partridges began to flap, but they angled their wings differently from 50 birds in flight. They aimed their flapping down and backward, using the force not for lift but to keep their feet firmly pressed against the ramp. "It's like the spoiler on the back of a race car," he explained, which is a very apt analogy. In Formula One racing, 55 spoilers are the big aerodynamic fins that push the cars downward as they speed along, increasing traction and handling. The birds were doing the very same thing with their wings to help them scramble up otherwise impossible slopes.60 Ken called the technique WAIR, for wing-assisted incline running, and went on to document it in a wide range of species. It not only allowed young birds to climb vertical surfaces within the first few weeks of life but also gave adults an energy-efficient65 alternative to flying. In the Chukar experiments, adults regularly used WAIR to ascend ramps steeper than 90 degrees, essentially running up the wall and onto the ceiling.In an evolutionary context, WAIR takes on 70 surprising explanatory powers. With one fell swoop, the Dials came up with a viable origin for the flapping flight stroke of birds (something gliding animals don't do and thus a shortcoming of the tree-down theory) and an aerodynamic function for 75 half-formed wings (one of the main drawbacks to the ground-up hypothesis)Q: What can reasonably be inferred about gliding animals from the passage? Answer Choices: (A)Their young tend to hop along beside their parents instead of flying beside them. (B)Their method of locomotion is similar to that of ground birds. (C)They use the ground for feeding more often than for perching. (D)They do not use a flapping stroke to aid in climbing slopes.
A: Among A through D, the answer is
(A)Their young tend to hop along beside their parents instead of flying beside them.
(B)Their method of locomotion is similar to that of ground birds.
(C)They use the ground for feeding more often than for perching.
(D)They do not use a flapping stroke to aid in climbing slopes.
Answer: 3