What are these flowering perennials with white flowers?

Question

What are these flowering perennials with white flowers (growing in a yard in Northeast Ohio)?

Answer 1

Well they're Yucca - I think they're Yucca flaccida rather than Yucca aloifolia (Spanish Bayonet) because the outermost leaves appear to be flopping outwards rather than remaining upright. Although I can't see any filaments dangling from the edges of the leaves, if there are lots of them, then its Yucca filamentosa. Pic of Yucca flaccida in the link below

https://www.rhs.org.uk/Plants/68112/Yucca-flaccida-Ivory/Details