Solution:

Let the base of the altitude from $C$ to $AB$ be $E.$ and let the base of the altitude from $D$ to $AB$ be $F.$ Also, let $BC = 10$ since we can assign any value. This yields the following diagram:

Then, let $FB = x$ and the altitude be $h.$ This means $$\begin{align*}AE &= 33-x-EF\\&=33-x-21 \\&= 12-x.\end{align*}$$

This suggests that: $$14^2 = (12-x)^2 + h^2$$ $$10^2 = x^2 + h^2.$$ Subtracting the equations, we get: $$96 = 144 - 24x$$ $$x = 2.$$ Then, we want to find $$\sqrt{ (21+x)^2+h^2}$$$$= \sqrt{21^2 + 42x + (x^2 + h^2) }$$$$= \sqrt{441+42\cdot 2 + 100}$$$$= \sqrt{625}$$$$=25.$$

Thus, the correct answer is B .