For the Past Week, Li Na Was Very Busy and Slept

For the past week, Li Na was very busy and slept very little. Li Na spent the entire week studying for an important exam. Li Na's grade on the exam would significantly affect her course grade, driving her to study hard. However, when Li Na took the exam, she felt she did not do as well as she should have given the amount of studying she did. For Li Na, her performance was likely MOST affected by:

A) lack of interest in the material being assessed.
B) poorer memory and reasoning than usual.
C) increased irritability and moodiness.
D) having less motivation to do well than usual.