I agree this seems impossible  how long do they expect the average 10year old to take on this?
The constant is the total number of shapes (8) and the number of circles increases from one black and one white to one black and 4 white, so would expect the answer to contain 8 shapes, one black circle, five white circles and two others. Both A and C fit that pattern
Triangles go 3,3,2,2 Squares go 3,2,2,1
so it's easily possible to argue the next box should contain 1 triangle, 1 square which is C as you chose
Including texture the sequence goes:
White triangles 2,1,1,1 White squares 1,1,0,0
Dotty triangles 1,1,1,1
Black squares 1,1,1,0
Stripey triangles 0,1,0,0 Stripey squares 1,0,1,1
 which suggests the next term should have just one stripey shape but no other clear pattern. I can see no reason for supposing that stripey shape should be a triangle again (as answer a implies) rather than c (as the OP prefers)  infact the "must have at least one of each shape" is a pretty good reason for choosing c
A badly written question IMHO which has nothing to do with intelligence, or creativity, or mathematical ability
And that's taken me a good 510 minutes.
