What does an electroencephalograph measure

A)  duration of sleep stages 
B)  glucose metabolism in the brain 
C)  electrical activity of the brain 
D)  variations in conscious awareness

Electroencephalograph

A device used to record the electrical activity of the brain, used in the diagnosis of neurological conditions and in research.

Electrical Activity

The movements of electrons or current within a system, often measured in the body or brain to assess function.