4. The sum of the interior angles of a polygon formed by cutting off a corner of a convex polygon is $2520^{\circ}$. Then the number of sides of the original polygon is ( ).
(A) 14
(B) 15 or 16
(C) 15
(D) 15 or 16 or 17
Answer: D.



The text above has been translated into English, preserving the original text's line breaks and format.