11. Two bees $A$ and $B$ start flying from the same starting point at the same rate. Bee $A$ first flies 1 foot north, then 1 foot east, and then 1 foot up, and continues to fly in this manner; bee $B$ first flies 1 foot south, then 1 foot west, and continues to fly in this manner. When they are exactly 10 feet apart, in which direction are the two bees flying?
(A) $A$ east $B$ west
(B) $A$ north $B$ south
(C) $A$ north $B$ west
(D) $A$ up $B$ south
(E) $A$ up $B$ west
11. A.

Taking the starting point of the two bees as the origin of coordinates, the southward direction as the positive direction of the $x$-axis, the eastward direction as the positive direction of the $y$-axis, and the upward direction as the positive direction of the $z$-axis, with 1 foot as the unit length, establish a spatial rectangular coordinate system.
From the problem, we know that the flight path coordinates of bee $A$ are
$$
\begin{array}{l}
(0,0,0) \rightarrow(-1,0,0) \rightarrow(-1,1,0) \\
\rightarrow(-1,1,1) \rightarrow \cdots
\end{array}
$$

After flying 6 steps, it reaches the point $(-2,2,2)$;
The flight path coordinates of bee $B$ are
$$
\begin{array}{l}
(0,0,0) \rightarrow(1,0,0) \rightarrow(1,-1,0) \\
\rightarrow(2,-1,0) \rightarrow \cdots
\end{array}
$$

After flying 6 steps, it reaches the point $(3,-3,0)$.
At this point, the distance between the two bees is
$$
\begin{array}{l}
d_{A B}=\sqrt{(2+3)^{2}+(2+3)^{2}+(2-0)^{2}} \\
=\sqrt{54}10 .
\end{array}
$$

In summary, when the two bees are exactly 10 feet apart, bee $A$ flies east, and bee $B$ flies west.