Which of the following exemplifies phonologically-conditioned allomorphic alternation?

過去式語素 -ed 隨前一音素變形：walked [t] (清音後)、played [d] (濁音後)、started [ɪd] (/t,d/後)。同一個 morpheme {-ed} 因語音環境產生三種形式，正是 phonologically-conditioned allomorphic alternation。