Answer:
A.
Step-by-step explanation:
The prepositional phrase is that phrase that consists of a preposition, the object, and words to modify the object. A prepositional phrase modifies either a verb or a noun.
In the given case, the correct usage of prepositional phrase to expand the sentence would be, "There are so many different paths through the Mirkwood Forest." The prepositional phrase "through the Mirkwood Forest" expands the sentence 'there are so many different paths'.
Therefore, option A is correct.