What is the polar form of the complex number $\;(i^{25})^{3} \;$ ?

Question

$(a)\; cos \large\frac{\pi}{2} - i sin \large\frac{\pi}{2}\qquad(b)\;cos \large\frac{5\pi}{2} + i sin \large\frac{5\pi}{2}\qquad(c)\;cos \large\frac{3\pi}{2} + i sin \large\frac{3\pi}{2}\qquad(d)\;cos \large\frac{\pi}{4} - i sin \large\frac{\pi}{4}$