Final answer:
The five unmarked vowel letters in the English alphabet are a, e, i, o, and u. These letters represent different vowel sounds in words.
Step-by-step explanation:
The five unmarked vowel letters in the English alphabet are a, e, i, o, and u. These letters represent different vowel sounds in words.
For example, the letter a can represent the sound in words like 'cat' and 'bat'. The letter e can represent the sound in words like 'bed' and 'pen'.
Similarly, the letters i, o, and u can represent different vowel sounds in various words.