Made when sediments fill in a cavity made when an object decayed and the sediments harden into rock

A fossil is formed when a plant, animal or other organism dies. The soft tissues of these organisms gets decomposed and degraded by decomposers present in the soil. The remaining hard and undecayed part like wood, shells, skeleton are left. These remains are covered by layers of soils. These layers of soil gets compacted to produce rocks. The rocks exhibit the dead remains are called as cast. A cast is also termed as mould fossil. It is the general form of the original organism.  

Therefore, the description: Made when sediments fill in a cavity made when an object decayed and the sediments harden into rock is cast.

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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