4. Which of the following is a possible number of diagonals of a convex polygon?
(A) 21 ;
(B) 32 ;
(C) 45 ;
(D) 54 ;
(E) 63 .
4. Ans: (D)
The number of diagonals of an $n$-side polygon is $\frac{n(n-3)}{2}$. Hence (D).