Answer:
C. Add a semicolon after corner
Explanation:
Because it has two distinct clauses, each of which may stand alone as a full sentence, this new phrase is a compound sentence. "Wildflowers grew in the back corner of the abandoned lot," the first phrase, is an independent clause since it includes a subject and a verb.
Because it has a subject and a verb, the second phrase, "Only the daffodils in the front were picked," is likewise an independent clause. A semicolon connects the two phrases, indicating that they are linked.
The new sentence would be "Wildflowers grew in the back corner of the abandoned lot; only the daffodils in the front were picked."