Which of the following is true of the description by Laureys 2005) of two separable aspects of consciousness in a healthy person:

A) Levels of awareness can vary but levels of attention remain constant
B) Levels of attention can vary but levels of wakefulness remain constant
C) Levels of awareness and levels of attention are always balanced across the three global states
D) Levels of attention and levels of wakefulness can vary across the three global states