Why are viruses called obligate intracellular parasites?
a. They must use a host cell's ribosomes to synthesize proteins.
b. They must use a host cell's nucleotides for transcription and replication.
c. They must use a host cell's amino acids to synthesize proteins.
d. They must use a host cell's metabolic enzymes and pathways to obtain energy.
e. All of the above.

they servive only in living cells.

Explanation:

the virus are connecting link between living and non-living. they are unable to perform life process outside the living cells. outside the living cells, the viruses behave as simple chemical so they are called as obligate intracellular parasite.

you are certainly talking about this picture:

a: is the label of the white square, it is showing the  replication fork, formed by helicase (d) ==> so it is the site of dna separation and replication 

b: is a new dna brand that is following directly the replication fork, so it is continuous ==> built continuously from 5' to 3

c: dna polymerase cannot replicate dna on its own, it needs the of their proteins, and one of them plays the role of a clamp which fixes  the dna with the dna template and increases  the processivity of the enzyme. ==>   stops polymerase from falling off the  template.

d: is the enzyme responsible for forming the replication fork (helicase) ==> unwinds and separates dna into two strands

e: is the delayed strand, it is built  in the opposite sense of the helicase, so dna will be built in fragments ==> built  fragments from 5' to 3 joins

and finally f: is the enzyme that builds  the new dna strand (dna polymerase) ==>   adds nucleotides to make a new dna helix.

credit: gradman555p98x9p

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