What is the most likely explanation for the poet's ending "Miracles" with this line?

What stranger miracles are there?

It's C or He wishes to encourage the reader the reader to see everyday things and events as miracles.

This poem of the celebrated American poet Walt Whitman is all about the beauty of the world which itself is a miracle. To Whitman everyday things are the miracles. The events that happen daily, the nature, the people. All of these things are miracles in themselves and he wants the readers to see too. That is why he as in the end what is stranger than things we see everyday.