3. Given three propositions:
(i) Rt $\triangle A B C, \angle A C B=90^{\circ}, C D$ is the altitude. Then $C D^{2}$ $=A D \cdot D B_{1}$
(ii) Rt $\triangle A B C, \angle A C B=90^{\circ}, D$ is a point on $A B$, $C D^{2}=A D \cdot D B$. Then $C D$ is the altitude of $\triangle A B C$;
(iii) $\triangle A B C, C D$ is the altitude, $C D^{2}=A D \cdot D B$. Then $\angle A C B=90^{\circ}$. The judgment of the correctness of these three propositions is
(A) All three propositions are correct
(B) Only proposition (i) is correct
(C) Propositions (i), (ii) are correct, (iii) is incorrect
(D) Propositions (i), (iii) are correct, (ii) is incorrect
3. $\mathrm{B}$ (Hint: For proposition (ii), consider the case where $D$ is the midpoint; for proposition (iii), consider the case where $\angle A B C>90^{\circ}$.)