6. For a given unit square, if its two diagonals and the lines connecting the midpoints of each pair of sides are drawn, figure 1 is obtained. Then, the number of pairs of similar triangles in figure 1 is ( ).
(A) 44
(B) 552
(C) 946
(D) 1892
6.C.

In Figure 1, all triangles are isosceles right triangles. First, let's count the number of triangles:

Classified by the length of the hypotenuse: there are 4 triangles with a hypotenuse length of $\sqrt{2}$; 8 triangles with a hypotenuse length of 1; 16 triangles with a hypotenuse length of $\frac{\sqrt{2}}{2}$; and 16 triangles with a hypotenuse length of $\frac{1}{2}$.
In total, there are 44 triangles, so the number of pairs is $\frac{44 \times 43}{2}=946$ pairs.