46. The global monitoring of influenza viruses, such as H1N1 and H5N1, is a primary focus of public health biology. Influenza viruses are classified based on two primary variables, hemagglutinin (H) and neuraminidase (N). Which of the following statements about influenza viruses is correct? (A) Influenza viruses are double-stranded DNA viruses that infect mainly humans. (B) H5N1 is currently classified as an avian flu that mainly infects birds and can cause severe disease in humans, but usually does not spread easily between people. (C) The "H" and "N" in H5N1 refer to the numbers of viral strains and enzymes, respectively. (D) The Influenza B virus is responsible for most influenza pandemics. (E) New influenza subtypes arise when small genetic mutations allow viral RNA segments to mix between different strains during infection of the same host cell.

13. Suppose a person begins breathing very rapidly while resting (hyperventilating), which of the following best describes how homeostasis is restored? (A) Rapid breathing decreases blood CO2 levels, thereby raising blood pH. The frontal cortex detects the change and reduces stimulation of the rib muscles and the diaphragm, thereby decreasing the breathing rate. (B) Rapid breathing increases blood CO2 levels, thereby causing the blood pH to drop. The hypothalamus detects the change and decreases stimulation of the rib muscles and the diaphragm, thereby reducing the breathing rate. (C) Rapid breathing decreases blood CO2 levels, thereby raising blood pH. The hypothalamus detects the change and reduces stimulation of the rib muscles and the diaphragm, thereby decreasing the breathing rate. (D) Rapid breathing increases blood CO2 levels, thereby causing the blood pH to drop. The medulla oblongata detects the change and reduces stimulation of the rib muscles and the diaphragm, thereby decreasing the breathing rate. (E) Rapid breathing decreases blood CO2 levels, thereby raising blood pH. The medulla oblongata detects the change and reduces stimulation of the rib muscles and the diaphragm, thereby decreasing the breathing rate.

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