I was solving the sample problems for my school's IQ society and there are some I don't get. Since all I get is a final score, I wanted to ask puzzling if someone might be able to make things clearer. For the problem that I've answered I'm writing down the answer and explanation below. I'm not sure if it's right though.
I believe the answer is C. For each column, move from top to bottom on each side (left/right) of the rectangle. If there are two occurrences of the black dot, it is cancelled out, so there's a blank in the bottom rectangle. If there's only one black dot, it is added to the bottom rectangle. So the right column is basically the same as the middle column apart from left/right being switched, hence the resulting image is the same.