A. 0

B. 2

C. 4

D. 5

### Solution(By Apex Team)

The average of the elements in the original set S is: $\begin{array}{l}\Large\frac{0+2+4+5+9}{5}\\ =\Large\frac{20}{5}\\ =4\end{array}$ If we remove an element that equals the average, then the average of the new set will remain unchanged. The new set after removing 4 is {0, 2, 5, 9}. The average of the elements is, $\begin{array}{l}\Large\frac{0+2+5+9}{4}\\ =\Large\frac{16}{4}\\ =4\end{array}$