(a) Why does DNA replication occur within a replication fork and not in its entire length simultaneously? (b) "DNA replication is continuous and…

Energetically very expensive process or there is requirement of high energy in the process of replication

DNA-dependent DNA polymerases catalyses polymerisation according to template strand only in one direction that is $\displaystyle 5$' → $\displaystyle 3$', On one strand with polarity

$\displaystyle 3$' → $\displaystyle 5$', the replication is continuous, while on other strand with polarity $\displaystyle 5$' → $\displaystyle 3$' the replication is discontinuous