All of the above are needed. Nucleotides are the basic building blocks of new DNA, ATP energy is needed because replication is an active process, and enzymes catalyze the reactions needed to carry it out (e.g. helicase to separate the strands to be replicated, DNA polymerase to build the new strands, and ligase to "glue" the fragments together).
It's the pull of gravity on an object.
Hope this helps!
