What letters must precede the suffix -ed for it to be pronounced as (ed)?

The correct choice involves the letters that, when they precede the suffix -ed, lead to its pronunciation as /əd/. The letters d and t are significant in this context because sounds ending in /d/ or /t/ allow for the ed suffix to be articulated in a specific way. When a verb ends with either a voiced consonant (such as d) or an unvoiced consonant (such as t), the blending of the sounds leads to the unique /əd/ pronunciation when -ed is added.

For example, take the verb "want," which ends in a t sound. When -ed is added to form "wanted," it is pronounced as /ˈwɒnteɪd/ and adheres to the phonetic rules for the /əd/ sound. Similarly, in verbs ending with d, such as "breathe," the past tense "breathed" maintains the /əd/ articulation.

Understanding this pronunciation pattern helps clarify why this particular answer is the most appropriate. The other options involve letter combinations that do not facilitate the /əd/ pronunciation when -ed is added, as they tend to transition to other phonetic sounds instead.