Question

Which are coplanar and noncolinar?

Answer 1

Coplanar means "lying on the same plane," while colinear means "lying on the same line." In this problem, all four points A, B, C, and D are coplanar - they all lie on the plane $\mathcal{H}$ - so we just need to find the points that lie on the same line. Though points C and B would be colinear if there was a line drawn between them, there's no such line in this problem, so we can rule that out. We notice one line drawn on the plane, and points A, C, and D lying on it, so we can say that points A, C, and D are both coplanar and colinear.