Using the given pka values, which of the following systems could be used to make a buffer with a ph of 7 (select all that are appropriate)
a. Acetic acid (pKa = 4.76) and sodium acetate (pKa = 9.24)
b. Phosphoric acid (pKa = 2.15, 7.20, 12.35) and sodium dihydrogen phosphate (pKa = 7.20)
c. Citric acid (pKa = 3.13, 4.76, 6.40) and trisodium citrate (pKa = 6.40)
d. Glycine (pKa = 9.60) and sodium hydroxide