**Core Concept**
The parietooccipital region of the brain is involved in processing visual information, and its electrical activity can be recorded using electroencephalography (EEG). When a subject is awake and has their eyes closed, the EEG waves in this region reflect a state of reduced cortical activity and decreased sensory input.

**Why the Correct Answer is Right**
When a subject is awake but not actively engaged in sensory processing (e.g., with their eyes closed), the parietooccipital region of the brain exhibits alpha waves. These waves have a frequency of 8-12 Hz and are characterized by a smooth, sinusoidal pattern. Alpha waves are thought to reflect a state of relaxed, closed-eyes attention, and are often seen in individuals who are awake but not actively engaged in sensory processing.

**Why Each Wrong Option is Incorrect**
* **Option A:** Beta waves are typically seen in states of active engagement, attention, or cognitive processing, which does not match the description of the subject being awake and eye-closed.
* **Option B:** Theta waves are often associated with states of drowsiness or sleep, which is not consistent with the subject being awake.
* **Option C:** Delta waves are typically seen in deep sleep or in individuals with severe brain disorders, which does not match the description of the subject being awake and eye-closed.

**Clinical Pearl / High-Yield Fact**
Alpha waves can be used as a marker for relaxation and reduced cortical activity, and are often seen in individuals who are awake but not actively engaged in sensory processing.

**Correct Answer: A. Alpha waves**