To accurately estimate genetic distance as a measure of the actual number of substitutions that have occurred one must adjust the observed fraction of substitutions because (select all that apply):

(A) Single substitutions are tedious to count and one wants to adjust for errors one make in counting.
(B) Parallel substitutions in multiple sequences obscure where changes have occured.
(C) Convergent substitutions result in changes in multiple sequences that would not be observed.
(D) One can have sequential substitutions in a sequence over time.