Degenerated neurons in certain parts of the brain have been observed in dogs with

Narcolepsy.
Basically what narcolepsy is the overwhelming uncontrollable urge to fall asleep in any place, at any time. It's a sleep disorder that doesn't really categorize sleep and wakefulness well.
I hope all is well and you pass! Good luck, rockstar! (:

The correct answer is a. we know this because n (hap) + n (hap) = 2n (dip).