The PK_a of a Compound Whose Acidic or Basic Form

The pK_a of a compound whose acidic or basic form absorbs UV or visible light can be determined spectroscopically since

A) l_max always decreases as acidic form is converted to basic.
B) the pK_a is the same as the pH at which half of the total absorbance increase occurs.
C) absorbance of the basic form is always twice that of the acidic form.
D) absorbance of the acidic form is always twice that of the basic form.
E) delocalization always leads to a decrease in acidity.