7. After cutting off a corner of a convex polygon, the sum of the interior angles of the resulting polygon is $2520^{\circ}$. Then the number of sides of the original polygon is ( ).
(A) 14
(B) 15
(C) 15 or 16
(D) 15 or 16 or 17
7.D.
$$
2520^{\circ}=(16-2) \times 180^{\circ} \text {. }
$$

After cutting off one corner, the number of sides of the polygon may remain unchanged, may increase, or may decrease.