Final answer:
The first-grade student who has attained the highest level of phonemic awareness is student B, who can orally segment the word wonderful into its individual sounds.
Step-by-step explanation:
The first-grade student who has attained the highest level of phonemic awareness is student B. This student can orally segment the word wonderful into won-der-ful. Phonemic awareness refers to the ability to identify and manipulate individual sounds (phonemes) in spoken words. By segmenting the word into its individual sounds, student B demonstrates a higher level of phonemic awareness compared to the other students.