In Dogs, the Fgf4 Gene Encodes a Protein That Regulates

In dogs, the Fgf4 gene encodes a protein that regulates bone growth, and in its normal chromosomal location, Fgf4 yields dogs with long legs. Which statement best explains the mechanism leading to a short-legged phenotype in dogs?

A) During retrotransposition, the Fgf4 gene loses two exons, resulting in a shorter mRNA.
B) A LINE is retrotransposed into the third exon of the Fgf4 gene, leading to a less functional protein that regulates bone growth.
C) The Fgf4 gene is retrotransposed into the middle of a LINE that contains mutated regulatory sequences that give abnormal expression of Fgf4.
D) During reverse transcription of the Fgf4 mRNA, an intron is included that inhibits expression of the Fgf4 gene.