Please Use the Following Information to Answer the Question(s) Below

Please use the following information to answer the question(s) below.
A man who is an achondroplastic dwarf with normal vision marries a color-blind woman of normal height. The man's father was 6 feet tall, and both the woman's parents were of average height. Achondroplastic dwarfism is autosomal dominant, and red-green color blindness is X-linked recessive.
-One of two major forms of a human condition called neurofibromatosis (NF 1) is inherited as a dominant allele, although it may range from mildly to very severely expressed. If a young child is the first in her family to be diagnosed, which of the following is the best explanation?

A) The mother carries the allele but does not express it at all.
B) One of the parents has very mild expression of the gene.
C) The condition skipped a generation in the family.
D) The child has a different allele of the gene than the parents.