Which consonant digraph is commonly recognized?

The digraph "th" is commonly recognized because it represents a specific sound that is distinct in English phonetics. This combination of the letters 't' and 'h' produces two different sounds: the voiced sound /ð/ as in "this" and the voiceless sound /θ/ as in "think." It’s important to note that "th" is unique as it does not correspond to a single letter sound in English, making it significant for learners, especially those acquiring English as a second language. Understanding and mastering this digraph is crucial for pronunciation and reading fluency, as it appears frequently in various words.

In contrast, the other choices—while they do represent common consonant clusters—do not function as digraphs in the same way. "Bl" and "st" are blends where each letter retains its original sound and is pronounced together, rather than creating a new sound. "Ea" functions as a vowel combination in English, leading to various vowel sounds but does not represent a consonant digraph. Thus, "th" is the choice that stands out as a recognized digraph with its own unique pronunciation rules.