Final answer:
Mismatch repair must occur before nucleotide excision repair. It corrects errors introduced during DNA replication by excising incorrectly added nucleotides and replacing them with the correct bases.
Step-by-step explanation:
Mismatch repair is the process that must occur before nucleotide excision repair. Mismatch repair corrects errors introduced during DNA replication by recognizing and excising incorrectly added nucleotides, replacing them with the correct bases. This repair mechanism is important for maintaining the integrity of the DNA sequence.