A teacher gave an impure sample of alum containing fine sand as impurity to a student. He asked him to recover pure alum from this sample. The correct procedure to be followed would be to :
A. dissolve the impure sample of alum in water, filter and evaporate the filtrate
B. dissolve the impure sample of alum in alcohol and filter
C. move a magnet over the impure sample of alum
D. dissolve the impure sample of alum in carbon disulphide, filter and evaporate the filtrate