OG详解-OG2 阅读 Q11

Choice A is the best answer because it presents an explanation about a helicopter that is directly supported by the text. The text states that Mars’s atmosphere is much less dense than Earth’s, and as a result, the air on Mars doesn’t provide the resistance required to support the blades of a helicopter built for Earth and to keep the helicopter aloft. In other words, a helicopter built for Earth can’t fly on Mars because of the differences in the two planets’ atmospheres. 
Choice B is incorrect because instead of stating that the blades of helicopters built for Earth are too large to work on Mars, the text indicates that the helicopter built to fly on Mars actually has even longer blades than a helicopter built for Earth. Choice C is incorrect because the text never addresses the role of gravity on Mars or on Earth; instead, it focuses on atmospheric conditions. Choice D is incorrect because the text doesn’t indicate that helicopters built for Earth are too small to operate in the conditions on Mars. In fact, the text states that the size of the helicopter built to fly on Mars is the same size as a helicopter built for Earth, even though it has longer blades that rotate faster.