Answer: B. Brain wave associated with sleep spindles.
Theta waves are brain waves that occur just when you are asleep or dreaming. These waves do not occur during the deepest of sleep but occur during light phases or just before waking up. Theta waves are used in making memories and also for processing information. Theta waves are faster than delta waves but slower than alpha waves. They fall at the end of the spectrum and are measured in the 4 to 8Hz range.