It is the dark, inaccessible part of our personality, what little we know of it we have learnt from our study of the dream-work and of the construction of neurotic symptoms. . . . We all approach [it] with analogies: we call it a chaos, a cauldron full of seething excitations. Which part of the mind was he talking about?

The correct response is the id.

Explanation:

According to the famous psychoanalyst Sigmund Freud, the id is the unconscious part of our mind that responses to impulses. Freud believed there were three parts to our psyche that help to form our personality and interact to guide or impulses and or thinking: the id, ego, and super-ego.  The id is that part of our psyche that responded to basic needs and desires and that seeks immediate satisfaction, or that gets pleasure from that immediate satisfaction. According to the famous psychoanalyst Sigmund Freud, the id is the unconscious part of our mind that responds to impulses. It is the earliest aspect of our personality to emerge. A baby's behavior is driven by the id dimension of the psyche for example, according to Freud.  

it's the under parts of the car