Which of the following would be the best first step for verifying the identity below?
tan^(2) y (csc^(2) y - 1) = 1

a. tan^(2) y (cot^(2)y) = 1
b. tan^(2) y (csc^(2) y -1) = sin^(2) y + cos^(2) y
c. (1/coy y)(csc^(2) y-1) = sin^(2) y + cos^(2) y
d. tan^(2) y ((1/sin y) - 1) = 1