Two paths r₁(t) and r₂(t) intersect if there is a point P lying on both curves. We say that r₁(t) and r₂(t) collide if r₁(t₀) = r₂(t₀) at some time t₀.

Which of the following statements are true?
(a) If r₁(t) and r₂(t) intersect, then they collide.
(b) If r₁(t) and r₂(t) collide, then they intersect.

(c) Intersection depends only on the underlying curves traced by r₁ and r₂, but collision depends on the actual parametrizations.