Why did Macmillan add iron rims to the tires of his bicycle?

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: D

Rationale: Strauss set up a net to ensure the safety of the workers in case of falls during the construction of the Golden Gate Bridge. Safety nets were essential to protect the workers from potential accidents or falls while working on the bridge. Choice A ('For suspension') is incorrect as safety nets were not used for suspension purposes but rather for worker safety. Choice B ('For balance') is incorrect as the balance of the bridge was maintained by other construction elements, not safety nets. Choice C ('For aesthetics') is incorrect as safety nets are not related to the visual appearance of the bridge but rather to the protection of the workers.

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: In the context of the passage, 'massive' is used to describe the size of the collision that formed the Moon, indicating something very large or huge. While 'dense' means closely compacted, 'impressive' means evoking admiration, 'huge' is the closest synonym to 'massive' in this context. 'Unavoidable' does not convey the same meaning as 'massive' in this sentence, making it incorrect.