Recessive Mutations in the Sxl Gene in Drosophila Are Lethal

Recessive mutations in the sxl gene in Drosophila are lethal in XX females because

A) sxl functions as a repressor of a male-specific dosage-compensation gene.
B) recessive mutations indicate an increase in sxl activity.
C) these mutations are the result of a loss of both X chromosomes.
D) sxl is required for transcription of male-specific genes.
E) recessive mutations are always lethal.