The Main Enzyme in DNA Replication, DNA Polymerase I Also

The main enzyme in DNA replication, DNA polymerase I also has a proof-reading exonuclease activity because it

A) needs to remove the DNA primer so that synthesis may be completed.
B) needs to correct pre-existing errors in the DNA before it is replicated.
C) needs to remove small DNA strands before it can begin the synthesis of the new strand.
D) needs to replace incorrect nucleotides inserted into the newly-synthesised strand.
E) detects mutations caused by sunlight and is able to remove them.