Correct Answer: D

Rationale: The correct answer is D. The author's primary purpose for writing the essay is to inform the reader about the stages of the water cycle. The essay discusses the various stages of the water cycle, including precipitation, runoff, evaporation, and condensation. Choices A, B, and C are incorrect because the essay focuses on explaining the water cycle stages rather than persuading the reader to conserve water, discussing the effectiveness of runoff, or analyzing different types of runoff.

Correct Answer: B

Rationale: The correct answer is B because it provides a comprehensive summary of the passage, explaining how the cardiovascular system regulates blood pressure through baroreceptors, chemoreceptors, and the kidneys. Choice A is incorrect as it only focuses on the heart and kidneys without mentioning the broader cardiovascular system. Choice C is incorrect as it solely emphasizes the role of baroreceptors in regulating blood pressure. Choice D is incorrect as it oversimplifies the role of chemoreceptors in monitoring oxygen levels without mentioning their impact on blood pressure regulation.

Correct Answer: A

Rationale: In the context provided, 'composed' means to consist of. The paragraph explains that a drop of water is composed of an oxygen atom and two hydrogen atoms. Therefore, the correct answer is A. Choice B, 'To be uniquely discovered,' is incorrect as it does not relate to the composition of a drop of water. Choice C, 'To be set apart,' and Choice D, 'To be surprised,' are also incorrect as they do not convey the meaning of 'composed' as it is used in this paragraph.

Correct Answer: C

Rationale: In the context of the second paragraph, 'phenomenon' refers to something significant and unusual, specifically describing the scientific phenomenon known as the Doppler Effect. This effect explains the change in frequency of sound waves when a source of sound and the observer are in relative motion. Choices A, B, and D are incorrect because they do not accurately reflect the meaning of 'phenomenon' in this context. 'Lifeless to the senses,' 'nonchalant,' and 'chemical in origin' do not align with the description of the Doppler Effect, which is a notable and uncommon scientific occurrence.

Correct Answer: C

Rationale: The correct summary of the passage is option C. The passage explains how the ECG systematically measures and records the 'wave of excitation' that occurs within the heart in three distinct steps, spreading from the SA node to the AV node. This summary effectively captures the main focus of the passage. Option A is incorrect because it only mentions the detection of electric currents in the body and recognizing abnormalities by medical staff, missing the key information about the 'wave of excitation' and its stages. Option B is incorrect as it focuses solely on the measurement and recording of unique electric currents on the body's surface, neglecting the specific process described in the passage. Option D is also incorrect as it provides a general description of how the ECG measures electric currents without emphasizing the specific stages of the 'wave of excitation' as detailed in the passage.