Step 1: Rather than deriving each correction from first principles, examine each listed item and ask whether it is a recognised, named correction taught for the standard soil hydrometer sedimentation analysis used to size silt and clay particles.
Step 2: Temperature correction (A) is required because the calibration chart and the viscosity value used in Stokes' law both assume a fixed reference temperature, and the lab temperature almost never matches exactly, so this stays in.
Step 3: Meniscus correction (B) is needed because a cloudy soil suspension hides the true liquid level, forcing readings at the meniscus top, while calibration is done in clear liquid where the true surface is visible, so this stays in too.
Step 4: Dispersing agent correction (C) is required because the chemical dispersant added to prevent flocculation changes the specific gravity of the suspension fluid slightly compared to plain water, and this must be subtracted out, so it also stays in.
Step 5: Pressure correction (D) has no established place in this procedure, there is no step that adjusts for atmospheric or fluid pressure, so it is discarded. That leaves exactly three valid corrections, (A), (B) and (C), option 3.\[\boxed{\text{Corrections: Temperature, Meniscus, Dispersing agent (A, B, C only)}}\]