OG3 阅读 Q27

Choice B is the best answer. Dial observed that as the Chukars raced up steep ramps, they "began to flap" and "aimed their flapping down and back-ward, using the force . . . to keep their feet firmly pressed against the ramp" (lines 49-53"to...explained"). Dial determined that the position of their flapping wings facil-itated the baby Chukars'traction on the steep ramps.
Choices A, C, and D are incorrect because the passage does not indicate that the Chukars'speed, alternation of wing and foot movement, or continual hopping motions facilitated their traction on steep ramps.