21. What is common in catheters and ventilators?

A. They bypass important defenses of the body
B. Bacteria responsible for associated infections are usually susceptible to antibiotics
C. They predispose patients to viral rather than bacterial infections
D. They are used primarily in neonatal intensive care units

22. An important host defense of human beings is a dense resident microbiota associated with

A. lungs
B. bladder
C. uterus
D. vagina

23. Lactoferrin helps to protect against pathogens by

A. sequestering Iron
B. blocking sebum production
C. lowering the pH
D. facilitating the growth of normal flora

24. The influenza vaccine is administered each year because

A. mutations in the viral hemagglutinin may allow the virus to evade the immune response elicited by previous vaccines
B. it is a polysaccharide vaccine that does not confer long-term protection
C. the vaccine is sufficiently toxic to make it necessary to administer only a small amount at any one time
D. none of the above

25. Which of the following disease is caused by DNA viruses?

A. Poliomyelitis
B. Yellow fever
C. Measles
D. Smallpox