[Solution] Proposition I is true. If it is known that the interior angles of a cyclic pentagon are equal, as shown in the figure on the next page, connect $A C, B E$, we can prove $\triangle A B C \cong \triangle B A E$, thus $A E=B C$.
Similarly, we can prove: $A B=C D, B C=D E$,
$$
C D=A E, \quad D E=A B .
$$

That is, $A B=B C=C D=D E=E A$,
which means the pentagon is a regular pentagon.
Proposition II is not true, just note that the four interior angles of a cyclic rectangle are all equal. Therefore, the answer is $(B)$.
$19 \cdot 14$ For the proposition
( I ) A cyclic pentagon with equal interior angles is a regular pentagon.
( II) A cyclic quadrilateral with equal interior angles is a regular quadrilateral. Among the following four conclusions, the correct one is
(A) Both I and II are correct.
(B) I is correct, II is incorrect.
(C) I is incorrect, II is correct.
(D) Both I and II are incorrect.