Can someone please help me? Identify the underlined element in the following passage from the novel Bleak House by Charles wingspanens.

“Fog everywhere. Fog flowing up the river, among green banks and meadows; fog rolling down the river, where it hangs defiled among the ships and buildings of a great (and dirty) city.”

Choices:
Infinitive phrase
Prepositional phrase
Sentence fragment
Absolute phrase

Question

Can someone please help me?  Identify the underlined element in the following passage from the novel Bleak House by Charles wingspanens.

“Fog everywhere. Fog flowing up the river, among green banks and meadows; fog rolling down the river, where it hangs defiled among the ships and buildings of a great (and dirty) city.”

Choices: 
Infinitive phrase 
Prepositional phrase 
Sentence fragment 
Absolute phrase

anonymous · Answer

Fog flowing up the river is underlined.

anonymous · Answer

Prepositional phase is what my brother thinks.

anonymous · Answer

I was thinking that but wasn't sure.  Thank you.  :)