Let’s take a closer look at the image to figure out which cup will fill up first based on how the liquid flows through the pathways.

When we examine the layout of the pipes leading to each cup, it becomes clear that many of the routes are either blocked or have obstructions.

Cup 3 is the first one without any blockage or obstruction on its path, so it will fill up before the others.

Therefore, the correct answer is Cup 3.