In what way do the swans in “the wild swans at coole” by william butler yeats represent eternity?

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,

The answer is d. prior knowledge. she breaks it into parts in order to figure out what other words have the same parts to the word and put the meanings together.