The earth’s core is made of an alloy of
a. iron and nickel.
b. copper and iron.
c. zinc and magnesium.
d. iron and zinc.

The correct answer is iron and nickel.

Earth's core is the hottest and deepest layer. It is made of two layers The outer core which forms the border of mantle and inner core is spherical ball which is made up of metal. The outer core is about 1400 miles thick and it is made up of combination of alloys (iron and nickel). Some other metals are also found there in trace amounts like uranium, platinum and gold.In the outer core these metals are found in solid form.

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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