Which of the following is true of aneuploidies in general?

A)A monosomy is more frequent than a trisomy.
B)45 X is the only known human live-born monosomy.
C)Some human aneuploidies have selective advantage in some environments.
D)Of all human aneuploidies, only Down syndrome is associated with mental retardation.
E)An aneuploidy resulting in the deletion of a chromosome segment is less serious than a duplication.