20. The equation $\left(x^{2}-5\right)^{2}=16$ has $(\quad)$ distinct real solutions.
(A) 0
(B) 1
(C) 2
(D) 4
(E) 8
20. D.
$$
\begin{array}{l}
\text { Given }\left(x^{2}-5\right)^{2}=16 \\
\Rightarrow x^{2}-5=4 \text { or } x^{2}-5=-4 \\
\Rightarrow x^{2}=9 \text { or } x^{2}=1 \\
\Rightarrow x= \pm 3 \text { or } x= \pm 1 .
\end{array}
$$

There are 4 solutions.