Look at the shape of a single leaf from the base to the tip. As you can see in the pictures, simple leaves appear as a single leaf, and compound leaves often appear to be several leaves coming from a single place in the stem or one leaf that has been subdivided.
All leaves are about the same shape, and no leaves were on top of the surface of the water (although some leaves may have been all the way to the surface, all the tops of all the leaves were wet)
When your plant was still in the water, some leaves were floating on top of the surface of the water and dry like a lily pad or some leaves near the top of the plant are a totally different shape (e.g. much wider) than those further down the stem.
If you don't think your plant is represented above try going back a level and choosing again.
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