B, can't use related equipment to judge two cups of liquid, unqualified;
C, the density of liquid can be measured with a balance and a measuring cylinder, and salt water and water can be separated by comparing the density, so the equipment in Group C meets the requirements;
D. Immerse the metal box of the pressure gauge into two cups of liquid respectively to keep it at the same depth, and observe the difference of liquid level in the U-shaped tube, which shows that the liquid has a higher density and is brine, and the equipment in Group D meets the requirements.
So choose ACD. ..