Answer: Leaving the last town in Mississippi.
Where the faces are so cold.
Step-by-step explanation:
Leaving the last town in Mississippi. —> who or what was leaving. The subject is missing.
Where the faces are so cold. —> Again, the subject is missing.
Just for reference, I’ll explain the next sentence. It is actually complete.
Go away! —> Sentences that demand an action often confuse students. The subject here is actually understood to be “you”.