Why are beavers called
nature's architects?

Beavers are the great architects of American ponds and streams. Beaver incisors never stop growing, and are self sharpening. The outer edge of the incisor is coated with hard enamel, while the inside is softer and wears down, keeping the cutting edge super sharp.

Explanation:

the only plants classified as non-seed producers are b) moss, fern, and liverwort!

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answer; (d) melting of sea ice;