Which of the following is true?

a.) a buffer is most resistant to ph change when [acid] = [conjugate base]

b.) the most effective buffers are those of strong acid/strong base pairs.

c.) an effective buffer has a [base]/[acid] ratio in the range of 10 - 100

d.) a buffer can not be destroyed by adding too much strong base. it can only be destroyed by adding too much strong acid.

e.) an effective buffer has very small absolute concentrations of acid and conjugate base.