Which of the following aqueous solutions are good buffer systems?
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a. 0.33 M acetic acid + 0.21 M sodium acetate .
b. 0.22 M hydroiodic acid + 0.25 M sodium iodide .
c. 0.10 M potassium hydroxide + 0.29 M potassium bromide .
d. 0.19 M hydrocyanic acid + 0.16 M sodium cyanide .
e. 0.33 M ammonium bromide + 0.34 M ammonia .

select all that apply