20. The number of integers that satisfy the inequality $x^{4}-51 x^{2}+50<0$ is ( ).
(A) 8
(B) 10
(C) 12
(D) 14
(E) 16
20. C.

Notice,
$$
\begin{array}{l}
x^{4}-51 x^{2}+50=\left(x^{2}-1\right)\left(x^{2}-50\right) \\
=(x-1)(x+1)(x-\sqrt{50})(x+\sqrt{50})<0 .
\end{array}
$$

Solving, we get
$$
\begin{array}{l}
x \in\{x \in \mathbf{Z} \mid x \in(-\sqrt{50},-1) \cup(1, \sqrt{50})\} \\
=\{ \pm 2, \pm 3, \pm 4, \pm 5, \pm 6, \pm 7\},
\end{array}
$$

a total of 12.