1. Calculate
$$
\sqrt{2018 \times 2021 \times 2022 \times 2023+2024^{2}}-2024^{2}
$$

The value is ( ).
(A) -12136
(B) -12137
(C) -12138
(D) -12139
- 1. C.

Let $x=2024$.
Then the original expression
$$
\begin{array}{l}
=\sqrt{(x-6)(x-3)(x-2)(x-1)+x^{2}}-x^{2} \\
=\sqrt{\left(x^{2}-7 x+6\right)\left(x^{2}-5 x+6\right)+x^{2}}-x^{2} \\
=\sqrt{\left(x^{2}-6 x+6\right)^{2}}-x^{2} \\
=6(1-x)=-12138 .
\end{array}
$$