Billy Is a Four-Year-Old Boy

Multiple Choice

Billy is a four-year-old boy. He has trouble walking and running like other children his age, and he sleeps through most of the day. He is diagnosed with multiple sclerosis. Billy's condition is the result of _____.

A) the abnormal lengths of the axons
B) a disruption in his myelin sheaths
C) the presence of an extra copy of chromosome 21
D) a disruption in his rapid eye movement sleep