3. In the plane, there are three point sets $M, N, P$:
$$
\begin{aligned}
M= & \{(x, y) \mid | x|+| y |<1\}, \\
N= & \left\{(x, y) \left\lvert\, \sqrt{\left(x-\frac{1}{2}\right)+\left(y+\frac{1}{2}\right)^{2}}\right.\right. \\
& \left.+\sqrt{\left(x+\frac{1}{2}\right)^{2}+\left(y-\frac{1}{2}\right)^{2}}<2 \sqrt{2}\right\}, \\
P= & \{(x, y) \mid | x+y|<1,| x|<1,| y |<1\} .
\end{aligned}
$$

Then
(A) $M \subset P \subset N$;
(B) $M \subset N \subset P$;
(C) $P \subset N \subset M$;
(D) None of (A), (B), (C) are true.
Answer ( )
3. (A)

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 evident that the vertices of the square are inside the ellipse. Therefore, the answer is $(\mathrm{A})$.