Question 18Circle $O$ has diameters $\overline{AB}$ and $\overline{CD}$ perpendicular to each other. $\overline{AM}$ is any chord intersecting $\overline{CD}$ at $P.$ Then $AP\cdot AM$ is equal to: $AO\cdot OB$$AO\cdot AB$$CP\cdot CD$$CP\cdot PD$$CO\cdot OP$
