It is just what it says: the subject alone, stripped from an other words associated with it.
Ex.
The fancy red sports car in my garage is broken.
complete subject = fancy red sports car
simple subject = car
B i think because you didnt give us the story
It's hard to answer without an excerpt you should have been provided. But I'll help you anyway. I suggest you to go with the second one: The speaker’s voice in the selection from “Clearances” is private and nostalgic.