The reason that there are Okazaki fragments during DNA replication is ultimately because:
A) Some parts of the chromosome are made of RNA and different polymerases have to be used
B) Polymerases can only synthesize in the 5' to 3' direction
C) There are only enough dNTP's to support quick replication on one strand, so the other strand lags behind it
D) It is necessary to "slow down" one of the strands so that replication does not occur before cells have a chance to grow