A 26-year-old woman with multiple sclerosis comes to the physician because of a recent relapse Examination of the eye movements shows slow adduction of the left eye with an associated right-beating nystagmus in the right eye. 

Which of the following is the location of the pathology that underlies this abnormality?
Abducens nerve palsy
Left medial longitudinal fasciculus
Right medial longitudinal fasciculus
Right oculomotor nerve