I took a Mensa online IQ test(<https://www.mensa.lu/en/mensa/online-iq-test/online-iq-test.html>) and encountered this question which I wasn't able to do:

[![enter image description here](https://i.stack.imgur.com/CjpNJ.png)](https://i.stack.imgur.com/CjpNJ.png)

This question is basically a visual analogy, where the first picture is to the second picture as the third picture is to the forth picture. This question is also found on these websites: <https://sifter.org/iqtest/> and <http://nzlweb.com/>. I know the answer is A and D but I cannot find a pattern that tells why the answer is A and D. Any help in this problem is appreciated. Thank you.