17. The diagram shows a pattern found on a floor tile in the cathedral in Spoleto, Umbria. A circle of radius 1 surrounds four quarter circles, also of radius 1 , which enclose a square. The pattern has four axes of symmetry. What is the side length of the square?
A $\frac{1}{\sqrt{2}}$
B $2-\sqrt{2}$
C $\frac{1}{\sqrt{3}}$
D $\frac{1}{2}$
E $\sqrt{2}-1$