What is the buffer range for effective buffering?

Between a 2:1 and 1:2 ratio of weak acid to conjugate base.

Between a 10:1 and 1:10 ratio of weak acid to conjugate base.

Between a 5:1 and 1:5 ratio of weak acid to conjugate base.

Between a 1:1 and 1:1 ratio of weak acid to conjugate base.