[FouRRaW]

Which of these solutions will form a buffer?

A. KOH and HCl
B. H2CO3 and NaHCO3
C. KF and HF
D. HCN and HF
 
Is it..
 B and C 
 A and B 
 C and D 
 B and D 

Only thing i can think of is that HCl and KOH are strong acids/ bases so they are eliminated from being a buffer solution.
   

[Yggdrasil]

You are correct that you can eliminate (A) as an answer.  A buffer will contain a weak acid and it's conjugate base (or a weak base and its conjugate acid).  Which of the remaining three choices fit this criteria?