It is might have been, because it is linking the subject, the reporter, with being correct about the approaching storm.
Structure .. that is the correct answer
Harper makes a connection between marriage and slavery when she mentions it that it “should only e a mere matter of bargain and sale…”
Their hearts have not grown old;
Passion or conquest, wander where they will,
Attend upon them still. I would say that this section of the poem indicate that the swans represent eternity ie saying that their hearts have not grown old and that they still have passion and a will for conquest indicates at least for now eternal qualities that they possess,