64. Which of the following bacteriophage is said to have banal symmetry?
A.T2
B.T4
C.T6
D.all of these

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65. Which of the following statements is correct?
A.Up to 10% of human tumours have a viral risk factor
B.Up to 40% of human tumours have a viral risk factor
C.Up to 30% of human tumours have a viral risk factor
D.Up to 20% of human tumours have a viral risk factor

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66. Which of the following are obligate intracellular parasites?
A.Chlamydia
B.Viruses
C.Rickettsia
D.All of these

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67.  Viruses can be purified based on their size and density by using
A.gradient centrifugation
B.differential centrifugation
C.precipitation
D.none of these

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68. 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

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