Determine whether the following statements are true and give an explanation or counterexample.

a. The hyperbola x²/4 - y²/9 = 1 has no y-intercept.

b. On every ellipse, there are exactly two points at which the curve has slope s, where s is any real number. 

c. Given the directrices and foci of a standard hyperbola, it is possible to find its vertices, eccentricity, and asymptotes.

d. The point on a parabola closest to the focus is the vertex.