Which of the following solutions is a buffer?
a) 0.10 M CH3COOH and 0.10 M CH3COONa,
(b) 0.10 M CH3COOH,
(c) 0.10 M HCl and 0,10 M NaCl,
(d) both a and c,
(e) all of a, b, and c.