Black swallows swooping or gliding In a flurry of entangled loops and curves:
The skaters skim over the frozen river.
And the grinding click of their skates as they impinge upon the surface,
Is like the brushing together of thin wing-tips of silver.

which describes the extended metaphor that the poet develops?
1. the poet compares skating to the process of making jewelry
2. the poet compares skaters to people who are knitting with yarn
3. the poet compares the motion and sound of skaters to that of birds
4. the poet compares that figures skaters make to those made by artists