Which of the following is a type of vowel digraph?

The correct answer, "ea," is a type of vowel digraph because it consists of two letters that together create one vowel sound. In the case of "ea," this digraph can represent different sounds, such as the long "e" sound in "bead" or the short "e" sound in "bread." Understanding vowel digraphs is an essential aspect of phonics instruction, as they play a crucial role in teaching students how to decode words and improve their reading skills.

In contrast, the other combinations do not represent vowel digraphs. "st," "nd," and "th" are consonant blends or digraphs that involve consonants working together to create specific sounds, but they do not include vowel pairs that combine to form a unique vowel sound. Recognizing vowel digraphs is important for students learning to read, as it helps them understand how different letter combinations can have varying phonetic outcomes.