6. Connecting the diagonals of the regular pentagon $A_{1} A_{2} A_{3} A_{4} A_{5}$ intersects to form a regular pentagon $B_{1} B_{2} B_{3} B_{4} B_{5}$, and connecting the diagonals of the regular pentagon $B_{1} B_{2} B_{3} B_{4} B_{5}$ again intersects to form a regular pentagon $C_{1} C_{2} C_{3} C_{4} C_{5}$ (as shown in Figure 1). Then, among the triangles formed by the line segments in Figure 1, there are ( ) isosceles triangles.
(A) 50
(B) 75
(C) 85
(D) 100