Which is NOT a Pythagorean trigonometric identity?

• a$\sin^2\theta + \cos^2\theta = 1$
• b$1 + \tan^2\theta = \sec^2\theta$
• c$1 + \cot^2\theta = \operatorname{cosec}^2\theta$
• d$\tan\theta + \cot\theta = 1$