Which of the following includes the cerebral cortex, thalamus, limbic system, and basal ganglia and governs functions such as learning, emotions, appetite, and consciousness?

hindbrain
midbrain
forebrain
split-brain

The part of the brain that includes all of the things that you've mentioned (so the cerebral cortex, thalamus, limbic system, and basal ganglia, etc.) would be the forebrain. 

The forebrain is an integral part of our brain and also at the same time the youngest part of our brain. 

Depression is lifelong, though you can get medication to with it. the difference between sadness and depression is that sadness lasts a little bit, depression last a long time and it goes on and off. people usually get depression through experiences they have been through, or genetics.