Found this picture in a random Whatsapp group. Someone said it's from one of the free online Mensa tests. Exact source unknown.
Here's my take:
c. The image is a 3d cylinder which is rotated about the x-axis (left-right). I get this from the point in the middle of the white circle which seems to indicate the tip of the tapered point. The pattern is "do nothing, front up $90^\circ$, rotate $180^\circ$, tip down $90^\circ$" and repeat, and read from left to right, top to bottom. This makes the next object c.
Here is the answer
Here is the method
The two symbols on the left and center in any row, add to create the right symbol. Once you add the symbols in the third row, you would have to perform arithmetic with the symbols that are shown in 1st and 2nd columns in 1st row and 2nd and 3rd columns in the 2nd row. If the symbols with the opposite orientation add, they cancel out. But if the symbol is being subtracted, that symbol's orientation must be reversed and henceforth added. If the symbols with the same orientation add, they simply produce the same symbol. This logic would give us option C.