5. Now there are two equally sized equilateral triangles, Alpha and Beta, each with a line segment connecting the midpoints of two sides. As shown in the figure, Alpha and Beta are positioned symmetrically left and right, but the line segments inside Alpha and Beta are asymmetric. Starting from the positions shown in the figure, Alpha moves horizontally to the right until it overlaps with Beta and then moves away. At each position during the movement, the figure formed by Alpha and Beta contains several triangles. In the position where the number of triangles is the greatest, the figure contains ( ) triangles.
(A) 9
(B) 10
(C) 11
(D) 12
Answer: $\mathrm{C}$.
You can draw all the cases and compare them to find the figure with the most triangles, and then count carefully, you will find there are 11, all the figures are as follows:

There is another way, if the two lines inside the triangle were not causing trouble, then this problem would be much simpler, let's start with a simpler case! When there are no two lines inside the triangle, these two triangles can have a maximum of
8 triangles during their movement (as shown in Figure 1). In this case, add the two lines according to the conditions in the question, without overlapping with the existing sides, at least 2 more triangles (as shown in Figure 2), and at most only 3 more (as shown in Figure 3).