At θ=0, the polar curve defined by r=θ2sinθ intersects the origin. Which description best characterizes the tangent line to the curve at that point?
a) The tangent is vertical only.
b) No horizontal or vertical tangent exists; the slope is a finite non-zero value.
c) The tangent is horizontal only.
d) Both horizontal and vertical tangents occur at the origin (a cusp).