Step 1: Idea:
A good proton acceptor must be the conjugate of a poor proton donor. So we look for the weakest acid among the parents.
Step 2: Rank the acids:
HCl, $HNO_3$ and $H_2SO_4$ ionise almost fully in water. Acetic acid ionises only a little.
Step 3: Rank the bases:
Reverse the order. $Cl^-$, $NO_3^-$ and $HSO_4^-$ have almost no tendency to pick up $H^+$ in water. Acetate does pick it up, giving $CH_3COOH$.
Step 4: Result:
Acetate is the strongest base listed.
Final Answer:
The strongest base is acetate.
\[ \boxed{B} \]