A 0.1967g unknown FAS sample was treated as described in the lab, diluted to 100.00 mL. 1.00 mL of the diluted sample was pipetted into a 100.00 mL volumetric flask, color-forming reagents were added, and:

a) The absorbance was measured.
b) The pH was adjusted.
c) The temperature was controlled.
d) The solution was filtered