For a differentiable polar curve described by r=f(θ), which of the following expressions is equal to dxdy in terms of derivatives with respect to θ?
a) \displaystyle \frac{dr}{d\theta}\sin\theta + r\cos\theta
b) \displaystyle \frac{\dfrac{dx}{d\theta}}{\dfrac{dy}{d\theta}}
c) \displaystyle \frac{\dfrac{dy}{d\theta}}{\dfrac{dx}{d\theta}}
d) \displaystyle \frac{\dfrac{dr}{d\theta}\sin\theta}{\dfrac{dr}{d\theta}\cos\theta}