What factor is LEAST likely to be causing his current difficulties at work?

You are working with a 29-year-old man who has a mental illness. He works as a janitor in a church in the mornings for 30 hours a week. The employer notices that he has recently started having difficulty staying on task and seems drowsy at work after 2 years of working there.

What factor is LEAST likely to be causing his current difficulties at work?
A . His medication
B . His work hours
C . His sleeping pattern/schedule
D . His general health/mental illness

Answer: B