1. Let the side length of the base of a regular quadrilateral pyramid be 2017, and the side edge length be 2000. Then the angle between the side edge and the base is closest to the difference in absolute value with option ( ).
(A) $30^{\circ}$
(B) $40^{\circ}$
(C) $50^{\circ}$
(D) $60^{\circ}$
-1. B.
Note that the projection of the apex of the cone on the base is the center of the base. Therefore, the cosine of the angle formed between the lateral edge and the base is
$$
\frac{\frac{2017}{\sqrt{2}}}{2000} \approx \frac{\sqrt{2}}{2} \text {, }
$$

but slightly larger than $\frac{\sqrt{2}}{2}$. Thus, the angle is slightly less than $45^{\circ}$.