What Does Mental Fatigue Mean or What Does It Imply

Multiple Choice

What does mental fatigue mean or what does it imply?

A) The brain is depleted of all of its glucose making thinking is very difficult.
B) I am too mentally fatigued to even bother answering this question.
C) The brain is full for information; no more room to conduct thinking, planning, and problem solving.
D) The person has difficulty planning, focusing attention, and changing behavior.