Answer:
Along the narrow forest trail, ferns and tiny wildflowers grew. (Third option)
Step-by-step explanation:
In the first choice, the first sentence is correct, but the second one is a fragment.
In the second choice, the sentence is not complete because it doesn't have a verb.
In the third choice, the phrase fragment is written correctly and as a complete sentence (so, it's the right answer).
In the fourth choice, both phrases are fragments because the first one does not include a verb, and the second one does not include a subject noun.
Hope this helps you out; have a fantastic day c: