Which One of the Following Cannot Act as a Buffer

Which one of the following cannot act as a buffer solution?

A) 0.40 M HNO₃ and 0.10 NaNO₃
B) 0.20 M NH₃ and 0.25 M NH₄Cl
C) 0.50 M HCN and 0.10 NaCN
D) 1.0 M KF and 1.0 M HF
E) 0.10 M HC₂H₃O₂ and 0.10 M NaC₂H₃O₂