Which of the following is an example of a mutation?

Responses
A A nucleotide is missing in a replicated DNA strand.A nucleotide is missing in a replicated DNA strand.
B A strand of DNA is used to create specific proteins.A strand of DNA is used to create specific proteins.
C A zygote receives two X chromosomes.A zygote receives two X chromosomes.
D A red blood cell loses its nucleus.

A A nucleotide is missing in a replicated DNA strand.