Answer:
A. In a dark corner of the attic were many unopened boxes.
Explanation:
When writing sentences in English, it is important to make sure that the subject agrees, in tense and person, to the verb. This allows the sentence to be logical. It also allows the reader to better understand the meaning of the words he is reading. In this example, the subject of the sentence is "many unopened boxes." As this is a plural noun phrase, the verb must also follow this form in order for it to make sense.
