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During normal breathing, what is the usual stimulus for a person to take a breath?

a. a decrease in pH of the cerebrospinal fluid

b. stimulation by norepinephrine

c. PCO2 in the blood drops below 40 mmHg

d. PO2 in the blood drops below 100 mmHg

1 Answer

2 votes

Answer:

a

Step-by-step explanation:

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