A. Fix plasticine at one end of a pencil to make a simple densimeter, so that it floats in two cups of liquid. The shallower the immersion, the greater the density of the liquid, which is brine, and the equipment in Group A meets the requirements;

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. ..