B: A circle with B as the center and BC=3 as the radius has two intersections with ray AC and can be made into two triangles.

C: Let A and B be vertices respectively. Let ∠A=60? ，∠B=45？ Two rays intersect at one point to form a unique triangle.

D: Make a circle with a diameter of AB=6, and choose any point C on the circle except A and B to make countless triangles.