3. In the plane, there are point sets $M, N, P$:
$$
M=\{(x, y) \mid | x|+| y |<1\}, N=\left\{(x, y) \left\lvert\, \sqrt{\left(x-\frac{1}{2}\right)+\left(y+\frac{1}{2}\right)^{2}}+\sqrt{\left(x+\frac{1}{2}\right)^{2}+\left(y-\frac{1}{2}\right)^{2}}\right.\right.
$$
$<2 \sqrt{2}\}, P=\{(x, y) \mid | x+y|<1, | x |<1, | y |<1\}$. Then
( A ) $M \subset P \subset N$
(B) $M \subset N \subset P$
(C) $P \subset N \subset M$
(D) (A), (B), (C) are all incorrect
3.【Analysis and Solution】As shown in the figure, $M$ is inside the square $B C E F$, $P$ is inside the hexagon $A B C$ $D E F$, and $N$ is inside the ellipse with $A D$ as the major axis. It is easy to know that the vertices of the square are inside the ellipse, so the answer is (A).