To begin with, I do not know whether this community is the appropriate place to ask this type of question and if it violate the purpose of the community, I beg to apologise.
I am preparing for an exam wherein I came up to with this question:
I couldn't understand the answer, and in my understanding, $A$ is the answer. My reasoning is that the pattern is left to right as the answer mention, we put the first image in the second image and cut off the bottom. Apart of this step, I lost and couldn't comprehend.