46. What is the main purpose of the passage?
Answer: C
The main purpose of the passage is to overview the causes of CF and how it is carried.
The passage provides a comprehensive overview of cystic fibrosis (CF), detailing both the genetic causes of the disease and how it is inherited through families. It explains the role of defective genes in the development of CF and highlights the prevalence of the CF gene among different populations.
A) To describe the causes of cystic fibrosis
While the passage does describe the causes of cystic fibrosis, focusing on the defective gene and the resulting thick mucus, this option does not encompass the full scope of the passage, which also discusses inheritance patterns. Thus, it is too narrow to represent the main purpose.
B) To explain how cystic fibrosis is passed down through families
This option accurately reflects part of the passage's content regarding inheritance, but it does not address the discussion of the causes of CF. Therefore, it is incomplete and does not fully capture the main purpose of the passage.
C) To overview the causes of CF and how it is carried
This option correctly identifies the passage's main purpose by encompassing both the genetic causes and the inheritance of cystic fibrosis. It captures the dual focus of the passage, making it the most comprehensive and accurate choice.
D) To review why some Americans have CF, but others do not
This option is misleading, as the passage does not specifically focus on the reasons for discrepancies in CF prevalence among Americans. Instead, it discusses the genetic basis and inheritance of the condition without delving into individual cases or variations in symptoms.
Conclusion
The correct answer, C, effectively encapsulates the dual focus of the passage on both the causes of cystic fibrosis and its inheritance patterns. In contrast, the other options either narrow the scope or misinterpret the content, failing to recognize the comprehensive overview provided in the passage. Thus, C is the definitive choice that aligns with the primary purpose outlined in the text.