Read the poem "A Jelly-Fish" by Marianne Moore. Then, answer the question that follows.

Visible, invisible,
A fluctuating charm,
An amber-colored amethyst
Inhabits it; your arm
Approaches, and
It opens and
It closes;
You have meant
To catch it,
And it shrivels;
You abandon
Your intent—
It opens, and it
Closes and you
Reach for it—
The blue
Surrounding it
Grows cloudy, and
It floats away
From you.

Which poetic form does Moore use in her poem?

Ballad
Free verse
Sonnet
Villanelle