O god, this had made it here too. Looks like F to me also. Idk how its anything else. Assuming the tops of all the containers are open to the atmosphere and the water is entering the system at a slow rate as depicted by the dripping faucet. If D wasnt blocked off then it would be G. If D was blocked off as it is and H wasnt blocked off then it would be H (assuming H is closed on the bottom because its coming up showing no bottom on my screen)
Another problem I have with these is.... Define "fill up".
If you define it simply as being until it can no longer hold any more water. Then you can also say technically A "fills up" first because it gets to a point when it is "full" which is why it passes water to tank B.
Yup, this is exactly how I see it happening in my head. Only way to argue against F is to define "Filled" as being something other than filling the entire square tank to the point that it over flows out of the top.