Filter aids like asbestos, kieselguhr, diatomaceous earth etc. are used to increase the porosity of the final filter cake & reducing the cake resistance during filtration. Filter aid is_______________?
A. Added to the feed slurry
B. Pre-coated on the filter medium prior to filtration
C. Separated from the cake by dissolving solids or by burning it off
D. All A, B. & C.