At What Point in the Following Titration Curve for a Weak

At what point in the following titration curve for a weak acid being titrated with a strong base is the pH equal to the pK_a of the acid? The x-axis scale goes from 0.0 mL to 20.0 mL.The sharp rise is at 10.0 mL.

A) 0.0 mL
B) 5.0 mL
C) 9.0 mL
D) 10.0 mL
E) 18.0 mL