Final answer:
The most suitable word to describe the student's singing, based on the description provided, is 'vigorous' as it indicates a robust and dynamic quality.
Step-by-step explanation:
The word that best describes the student's singing, as mentioned in the phrase 'His singing is bright and virile, and he is dramatically fearless,' is vigorous.
The word 'virile' indicates a masculine energy and strength, and when combined with 'bright and... fearless,' it suggests a robust and dynamic quality.
Therefore, the best choice out of the provided options is 'vigorous,' which means being strong, healthy, and full of energy.