26. Which of the following are obligate intracellular parasites?

A. Chlamydia
B. Viruses
C. Rickettsia
D. All of these

27. Viruses can be purified based on their size and density by using

A. gradient centrifugation
B. differential centrifugation
C. precipitation
D. none of these

28. The extracellular phage number increases until a constant titer at the end of the multiplication cycle. This time interval is termed as

A. eclipse period
B. rise period
C. latent period
D. burst size