What trait most likely evolved in ferns that was not present in the earlier groups?

We need the options to answer fully, but I can do my best.

Although the fossil record shows that ferns originated more than 360 million years ago, the radiation of the polypod ferns occurred after the rise of the angiosperms. 

Many of the fern species present today are likely to have evolved to occupy habitats newly created by the development of angiosperm forests.

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