Correct Answer: A

Rationale: The correct answer is A: 'What we know about the Moon and its differences from Earth.' The passage discusses various aspects of the Moon, including its origin, gravitational influence on Earth, physical characteristics, lack of atmosphere, and surface features. It provides insights into what humans know about the Moon and highlights its differences from Earth. Choice B is incorrect because while the passage does compare certain aspects of the Moon and Earth, it primarily focuses on the Moon itself rather than a direct comparison. Choice C is incorrect as the passage briefly mentions the Moon's effect on Earth in relation to tides but does not primarily focus on this aspect. Choice D is incorrect as the origin of the Moon is mentioned in the passage, but it is not the primary focus of the text.

Correct Answer: B

Rationale: Macmillan added iron rims to his bicycle tires to enhance their durability and make them last longer. This innovation aimed to prevent the tires from getting worn down quickly. Adding weight to the bicycle (Choice A) was not the purpose of adding iron rims. While adding iron rims could potentially reduce the bumpiness of the ride (Choice C) by providing more stability, the main objective was to improve tire longevity. Similarly, reducing the level of fatigue during the ride (Choice D) was not the primary reason for adding iron rims.

Correct Answer: D

Rationale: In the context provided, 'defective' means faulty, referring to the gene that causes cystic fibrosis (CF). The passage explains that CF is caused by a defective gene, resulting in the production of abnormally thick and sticky fluid. The word 'defective' suggests that the gene is not functioning correctly, leading to the symptoms associated with the disease. Therefore, 'faulty' is the correct choice. The other options, 'unusual,' 'remarkable,' and 'postponed,' do not accurately capture the meaning of 'defective' in this context and are therefore incorrect.

Correct Answer: A

Rationale: The correct answer is A: 'What we know about the Moon and its differences from Earth.' The passage discusses various aspects of the Moon, including its origin, gravitational influence on Earth, physical characteristics, lack of atmosphere, and surface features. It provides insights into what humans know about the Moon and highlights its differences from Earth. Choice B is incorrect because while the passage does compare certain aspects of the Moon and Earth, it primarily focuses on the Moon itself rather than a direct comparison. Choice C is incorrect as the passage briefly mentions the Moon's effect on Earth in relation to tides but does not primarily focus on this aspect. Choice D is incorrect as the origin of the Moon is mentioned in the passage, but it is not the primary focus of the text.

Correct Answer: C

Rationale: The correct answer is C. The passage aims to provide an overview of cystic fibrosis (CF) and how it is inherited. It explains that CF is passed down through families due to a defective gene, detailing how this gene affects the body and who is most commonly affected by the disease. Choices A, B, and D are incorrect because the passage does not solely focus on describing the causes of CF, explaining how it is passed down through families, or reviewing why some Americans have CF while others do not. Instead, it provides a broader perspective on CF and its inheritance.