u/Fresh-Weakness-3769

From what I thought gauge pressure was pgh, with h being the height of the fluid above it, and it was mostly represented with P(bot) = P(top) + pgh. So I thought that here, point D had to be greater than C, since it has far more mercury, a denser fluid, right above it. Yet not only was that not an option, C and D are equal just because they are of the same vertical height? So does h just have absolutely no bearing of "fluid above/below", what does it even mean? The AP Exam is tommorow and I still have no idea what Absolute, Gauge, and Atmospheric pressure, are/mean in different contexts because we had little time to learn.