Although the vast majority of women who inherit a single copy of an X-linked recessive disease allele are not affected by the disorder, a small percentage of women do display the disease phenotype. Which of the following could explain this rare phenomenon?

A. X-inactivation that favors inactivation of the normal X chromosome
B. incomplete penetrance of the X-linked recessive allele
C. Turner syndrome (a sex-chromosome aneuploidy in which women have only one X chromosome)
D. multiple alleles of the X-linked recessive trait