Select all of the following solutions that would form a buffer when they were mixed.

a. A solution that is formed when 0.33 moles of NaF is mixed with 0.39 moles of HCI. Assume the final volume is 1.0 L

b. A solution that is formed when 0.44 moles of HCOOH is mixed with 0.44 moles of KOH. Assume the final volume is 1.0 L.

c. A solution that is formed when 0.73 moles of CH3COOH is mixed with 0.39 moles of NaOH. Assume the final volume is 1.0 L

d. A solution that is formed when 0.52 moles of NaNO2 is mixed with 0.24 moles of HCl. Assume the final volume is 1.0 L

e. A solution that is formed when 0.23 moles of CH3CH2COOH is mixed with 0.49 moles of NaOH. Assume the final volume is 1.0 L