Correct Answer: B

Rationale: In the context of the given extract, 'evolved' means to gradually develop. The systems in the body have evolved over time, indicating a gradual development and adaptation. 'To spread,' 'to revolve,' and 'to shift' do not capture the idea of a gradual development as portrayed in the text, making them incorrect choices.

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: C

Rationale: The author's primary purpose in writing the essay is to inform the reader about how an electrocardiograph reads the electric currents emitted by the heart. Choice A is incorrect because there is no attempt to persuade the reader to have an ECG. Choice B is incorrect because the essay is focused on providing information rather than entertaining with a heartwarming story. Choice D is incorrect as the essay does not primarily analyze the difference between the SA node and the AV node; instead, it focuses on explaining how an electrocardiograph reads electric currents from the heart.

Correct Answer: D

Rationale: In this context, 'ideal' means perfect. The human body provides a perfect environment for many microbes, as stated in the extract. It is the immune system's role to keep these microbes out or destroy them. The other choices are incorrect: 'thoughtful' does not fit the context of the sentence, 'confined' and 'hostile' are not synonymous with 'ideal' in this context.

Correct Answer: B

Rationale: In the context of the given extract, 'evolved' means to gradually develop. The systems in the body have evolved over time, indicating a gradual development and adaptation. 'To spread,' 'to revolve,' and 'to shift' do not capture the idea of a gradual development as portrayed in the text, making them incorrect choices.