Normal Males (XY) and Klinefelter Males (XXY) Both Possess Only

Normal males (XY) and Klinefelter males (XXY) both possess only one active X chromosome. Nonetheless, there are clearly phenotypic differences between the two. What is the MOST reasonable explanation as to why such differences exist?

A) The Y chromosome has higher gene expression levels when two X chromosomes are present compared to one X.
B) The Y chromosome has lower gene expression levels when two X chromosomes are present compared to one X.
C) Some genes remain active on inactive X chromosomes so XXY males would have higher expression levels for these genes compared to XY males.
D) XXY males exhibit a higher rate of problems during mitotic divisions than XY males.
E) XXY males don't have a copy of the SRY gene.